engine and transmission change
 

I am currently driving a 91 1 ton 2 wheel drive dually. I picked it up pretty cheap for the main porpose of i hav a 93 2 wheel drive that i wrecked, and had thought if things went south on the 91 i could swap motors and or transmissions. So far i hav two problems transmission is pretty well shot n the 91, and it will also only run 65 mph. It has 3.55 rear end and i know it should run faster than that also it only gets about 15 mpg. They other one before it got wrecked ran 85 with 4.10 and got approximately 22. So my questions are, any advice on the sweed problem, and will the transmissions swap out easily? Also how difficult would it be to swap motor and transmissions altogether?

The 4.10 1st Gens seem to get better mileage on average for some reason. ALot of fuel goes out the tailpipe as black smoke in start-stop driving and getting up to speed over and over again. 4.10 is better at that. Mine averages around 20 in mostly highway driving if I keep my foot out of it, and it's a 4x4. I think you need to drive the dually unloaded nothing but highway to see decent mpg out of it.

Highway miles are mainly what I drive. Bout thirty a day. I know my other truck was turned up quite a bit, would that hav anything to do with that part of it?

Does the 91 have an overdrive trans?

It's standard but its messed up, within the week ill hav to swap them out.