Yup, the 5.9 was an option, but they weren't real popular.
They do suck gas...Off the showroom floor I got 12-13 avg MPG. After a free flowing intake, a homemade y-pipe, and bigger exhaust I averaged 15-16 mpg. Better wires and plugs are a must for that engine to wake it up. The best overall mpg I got was 20 mpg on a long trip.
As far as the trans goes...I don't know about the autos; but I trashed my manual at 60K. I had something similar to Cal-track bars in the rear and would launch it hard at the dragstrip. It finally went on the street between a 1-2 shift. I snapped and sheared off just about everything in the case. Since they only made the MT/V8 combo for the first year, that trans was rare, and very expensive to fix. With me pulling and installing the new trans it cost over $3K! They couldn't even get me the original gearing. They swapped the guts out of a Ram 5 speed into my case, which was ok because of the steeper gears.
Also, a 255/65/15 is a perfect fit on those rims, and looks awesome. I lowered mine 3"/5" drop with Nitro shocks, and it handled WAY better than the GP does.