Hy 57DanR, please remember to tell us the size (series designation) of the truck your are asking questions about. There are many truck sizes which have dual rear wheels. If the truck is a one ton (3800) then the rear axle is either an HO52 or HO72. The highest speed gear ratio available for those rear axles is 4.11 to 1, there are many threads on this website about swapping this gear set into your housing if you do not already have that ratio of gears in your rear axle. As to the 700R4 swap, that could be a bit more complicated, the original engine/transmission was supported at the front of the engine and the rear of the engine. Engines with a 700R4 attached were supported on the side of the engine and at the rear of the transmission, so to swap in the 700R4 and do the job with the least strain on the components you should install engine side mounts on your chassis and purchase/ fabricate a transmission support crossmember to support the rear of the transmission. You should be able to find an output yoke for the 700R4 that will take the same "U" joint as your stock driveshaft, then it is just a matter of getting the correct length of driveshaft made up. A word of caution with the 700R4, this transmission requires a very specific throttle pressure adjustment and travel through the range of throttle movement, failure to have this adjustment work correctly will allow the transmission clutches to slip and ruin the transmission in short order, hope that helps
