[piecesparts]

I am here to tell you that the 3.08 gears and a change to a OD tranny (700 R4 or 200 R4) is not the wisest thing that you could do. There is a breaking point for a GM V-8 motor as to the efficiency. That point appears to be around 2000 to 2100 RPM. I had 3.42 gears in my truck and added a 700 R4 tranny to it and the mileage worked out to about 15 MPG on the highway (this is with a stroked 383 motor). I put in 3.73 gears to get better acceleration and to manage the larger cam in the 383 better and I lost about 1 MPG total. I have no complaints there.

However; on my Son's truck we had a 350/350C combo and switched it to a 700 R4 and lost MPGs. He had the 3.08 gears. The truck was running down the freeway at 1900 RPM at 70 MPH and this created a condition og lugging the motor when approaching hills and the cruise control was overworking itself constantly. We changed his rear end gears to 3.73 and picked up 2.5 to 3 MPG by getting the RPMs up to about 2400 to 2500 at 70 to 75 MPH and gained responsiveness as an extra. Both of our trucks are SWB mid eighties trucks, but that would include about the same weight and size as yours. There are computations that you can use to get a plan for which size tires and tranny combo you would want to get to the right RPMs at whatever speed you drive the most. That is what I used to get the trucks wwe have figured out.