Well if it was built anything like the 360 (5.9L V8) then it was built to last. And the V10 in the rams did not have that much torque (a little over 400 ft.lbs) so I wouldn't be worried about the tranny handling it. As long as it wasn't abused you should be good

 

The transmission on my V10 gave up at 70k but it was an old 1995 model. It is my understanding that the transmissions got better sometime after that. As far as gas mileage goes it got about 12mpg my matter where or how I was driving. FWIW, a good friend of mine is actually the engine engineer that designed the heads for the V10 engine and he says that the engine is built to last. Mine carried very low oil pressure from the day it was new. As near as I can remember I think that he told me something about it being a high volume/low pressure system thus that was expected.