It's a story we've heard before, but a pretty good one: Sales are up, products are improving, and buyers have many choices of trucks to do their hauling jobs

, even if prices have climbed, especially for diesels.

Builders of North American conventional-cab midrange trucks (Chrysler, General Motors, Ford, Freightliner, Hino, Kenworth, Peterbilt and Navistar International) say 2011 sales are better than 2010, sometimes substantially so. And 2010 was better than 2009. This reflects a slowly improving economy and the need to replace aging trucks that users hung onto through the recession.

Importers (Hino, Isuzu, Mitsubishi Fuso and UD) generally report healthier business situations with their low-cab-forward models, with exceptions. One said it's seeing lots of interest, but some buyers, spooked by an uneasy business climate, are shying away from ordering trucks.

Domestic and imported trucks got EPA 2010-legal diesels this year or last, and like their Class 8 cousins, the new diesels carry hefty upcharges. The higher prices have made gasoline engines more popular in lighter-duty trucks. Ford will soon offer its 6.8-liter gasoline V-10 in the F-650, and it can be equipped to burn propane. A compressed natural gas engine is offered in the F-250. And Isuzu has resumed offering an NPR Gas model using General Motors' 6-liter gasoline V-8.

But if you haul or pull heavy loads or run a lot of miles, a diesel still does it better. So diesels remain the preferred power in the upper end of Classes 3 to 7. Diesels are the only engines available in most models from the importers, because that's what's used in trucks in their home countries.

Diesels in most trucks now use selective catalytic reduction to meet 2010 emissions regulations, along with the diesel particulate filters that appeared in 2007. Navistar alone has avoided SCR, and its executives credit its "in-cylinder only" approach to 2010 emissions limits for helping it to achieve greater market share in Classes 6 and 7. They say buyers like the idea of not having to bother with diesel exhaust fluid, and upfitters like the absence of fluid injection equipment because it leaves more room on the chassis for mounting bodies.

Classes 6 and 7 have shrunk somewhat as users either went to lighter, less costly trucks or quit using midrange models entirely, Navistar says. Some have gone to Class 5 trucks whose drivers don't need commercial driver's licenses, except in New York or if they haul hazardous materials. Others moved into "Baby 8" trucks, which have beefier chassis but are powered by midrange-size engines.

Most domestic builders offer Baby 8s. Paccar siblings Kenworth and Peterbilt recently expanded their product lines with them. KW's T440 and T470 trucks start at the top end of Class 7, with gross-weight ratings of 33,000 pounds, but most are built with heavier axles and/or tandem rears that push them into Class 8. A recently introduced model from Peterbilt, the 382, is similarly outfitted. The 8.9-liter Cummins ISL9 is their largest engine. These join the builders' previous but recently updated Class 5, 6 and 7 models that use Cummins-made Paccar PX diesels.

Mack and Western Star also announced Baby 8 conventionals early this year. Western Star believes its 4700, which is now going into production, will provide a healthy boost to its overall sales. Top executives in the Daimler organization see a trend toward this type of vehicle by several types of users who want heavy duty capabilities with lighter and less costly but still adequately powerful engines.

Mack sees the same trend, so came out with its Granite MHD, for medium-heavy duty. Like others in this category, the Western Star and Mack trucks use the Cummins ISL9.

Freightliner continues with its Business Class M2 series in Class 5 to 7, but is in the process of splitting general hauling models from vocational versions with the expanded SD (for severe duty) series. New this year is the medium-duty 108SD, which will gradually take sales that have been directed to the M2-106V (for vocational). The new heavy 114SD will take over from the current M2-112V, which is usually a Class 8 model. The M2-Vs will eventually be phased out.

At the other end, Navistar has expanded downward with its Class 4 and 5 TerraStar conventional. It wants some business now held by Ford, by far the market leader with its F-450 and F-550. Navistar thinks its TerraStar is superior, with features such as a tilt hood, a roomy upright cab and a medium-duty-based chassis. Its MaxxForce 7 V-8 diesel was extensively redesigned for 2010 and doesn't need SCR. By mid 2012 there'll be a 4x4 option; it was supposed to be out early this year, but it was delayed while Navistar switched suppliers for the front-driving axle and transfer-case.

Ford reports sales increases of 110% for its F-350, F-450 and F-550 conventionals. It has suitably updated them to meet the latest exhaust emissions limits and to keep the trucks competitive in the marketplace and useful to buyers. The main engines now are its 6.2-liter gasoline V-8, 6.8-liter gasoline V-10 and the company's own 6.7-liter PowerStroke V-8 diesel.

Ford says sales of its heavier F-650 and F-750 are up by 15% over last year. For now they are diesel-only, with Cummins' ISB in several ratings as the offering. Soon it will add gasoline power to the F-650 in the form of the V-10, which can be upfitted to burn propane. This was requested by customers and dealers. Orders for a gaseous-fuel prep package - mainly hardened valves and valve seats - have more than doubled, from 3,500 last year to 8,000 this year.

Ford is still looking at the possibility of adding tandem rear axles and beefier chassis and suspension components to create an F-850, but nothing is planned.

Ford announced it will move production of its F-650 and F-750 from Mexico to the U.S. The switch will take work done by Navistar employees in Escobedo, Mexico, and give it to United Auto Workers members in Avon Lake, Ohio. This is the result of a new contract just ratified by UAW members.

(The contract will also see UAW members begin building the European-style full-size Transit van, also at the Avon Lake plant. The Transit will gradually replace the E-series van, which will be phased out over the rest of this decade, Ford said. It already sells the compact Transit Connect, which is built in Turkey, in North America.)

Current F-650 and F-750 models use Ford cabs and the Cummins ISBs on Navistar chassis. Ford isn't saying what it will use for a chassis, or if other components will change. But it will end the Blue Diamond joint venture under which Navistar has built the Ford mediums at Escobedo. This is a logical outcome of the soured relations between the two companies since the dispute over the PowerStroke diesel and Ford's going its own way with its own engine.

General Motors remains in medium-duty by way of its Chevrolet and GMC 3500 series chassis-cab models with either 6-liter Vortec gasoline or 6.6-liter Duramax diesel, both V-8s. For 2012 the HD models get higher tow and payload ratings, both claimed to be "best in class." Rumors about GM returning to Class 4 and 5 have quieted, and GM execs say that while they continue to look at possibilities, they have nothing to report on it.

Ram, Chrysler's relatively new truck brand, also reported sales increases, and though it's more modest at 11%, it's still in the right direction.

Ram recently announced a 30,000-pound gross combination weight rating for its Heavy Duty 4500 and 5500 chassis-cab models with the Cummins Turbo Diesel. Up from 26,000 pounds GCWR, the MaxTow rating is made possible by recalibrated software for the Aisin 6-speed automatic transmission and a 4.88 axle ratio. A stronger transf