[piecesparts]

I would suggest a slight rethink on a 700R4 with an output number like .075 and a 3.08 geared rear end. I had a combo like that in my son's truck and the gas mileage really stunk bad. We went back to a 3.73 geared rear end and got back 2 MPG and some change. The RPMs were so low that in the hills of Kansas, with the 3.08 gears that we were working the truck's engine a lot to make a decent trip down the highway. We were also running a smaller tire diameter than most trucks and if you go taller than the 26" tires that we had, the RPMs will be lower, yet. I would think that a 3.42 gearing or the 3.73 will give you what you would want, but you neeed to decide what RPM you want to run at and what kind of driving you will be doing.

I am running a 385 stroker motor, with a 700 R4, 3.73 posi Eaton 12 bolt and 28" tall tires on the truck in my avatar. I am getting a good 15 MPG with an approximate 400 HP engine and a good solid acceleration. At 75 MPH on the highway, I am running around 2500 RPM and I could drop that another 150 RPM with a taller tire install. I would hope that you can do better with your plan, but I have two trucks that are relatively the same in size and setup and they are getting about the same mileage. The Son's truck suffered bad with the 3.08 gears and the OD tranny, so we copied my stroker setup.