What gear ratio does the truck have now, 3.92 is the tow gear in a Ram 1500 most came with a 3.55 if it was a dealer stock order. Being a 2WD truck the cost should be under $2000 out the door. I would go to a shop that does driveline only work if it were me. The other option is a complete rear axle swap from a 3.92 truck with low miles. I did this once to a Nova I owned was a lot easier then changing out the gears IMO.
As for the tire and wheel size not sure how much real help you would get going that route.
Don
