I had 3.55s in my Ram 4x4 with the 4.7 V8. For what I used the truck for it did alright but, I will tell you my combination was slower than early 2000s 4.3L V6 GMC Sierra 2wd work truck. I believe if not all Dakota V8s came with the 9 1/4 differential. You could go with a 4.56 gear but, I think at 70 mph your rpm will be 2500 rpm at minimum depending on tire and wheel size.