I have an 87 3/4 ton with stock LT235/85R16 tires, towing pkg (HD rear springs) and running boards. It came with 4.10 gears and a TH400. It also has a GV overdrive unit, but it still screams on the highway. I want to lower the RPM's to get better milage and the easiest way I can think of doing this is to lift it with bigger tires. Are 33's big enough to make a difference? or do I need 35's? I use this truck to tow, so I don't want to go too big. And what size lift would I need for 33's and/or 35's?