I had an 01 Dakota 4x4 with the 4.7, had 93K when I bought it and had like 150K when I sold it if I remember right. During the time that I owned it the only things I had to replace besides the normal wear n tear stuff was injectors (2 were leaking but I replaced all 8), brake light switch, radiator, thermostat housing seal & had the rear end rebuilt after the clutches gave out. That truck went through its paces and held up suprisingly well to the beating I gave it, my friends used to call me DK (drift King):redneck:
The 4.7 got good gas mileage too, I calculated my mileage one time going to the dunes with a quad, kx250 & crf50 in the back & I was averaging 22.5 (driving conservatively). Normal driving I would average around 17-18, but mine also had taller gearing.
Now that I think of it, I dont think I ever had the tranny serviced while I had the truck & never had any problems with it slipping. I never really towed anything heavy with it, I think the heaviest thing I ever towed with it was my Honda Civic HB on the flatbed but often hauled bikes/quads in the back or on the flatbed.
I actually miss that truck, it had nice power for a mid size truck and was very comfortable to drive. If you were going to replace the engine I would see what is needed to throw the 5.2 (318 CI) in there, much better engine and quiet a bit more power, I think they even put the 5.9's in some of the dakotas as well.