52Carl,
With the 338 gears and 27” tires the truck doesn’t really drive much differently then it did with the 390 gears, except that I can cruise at 60 MPH at 2700 RPM. The T-5 is probably the optimal setup but I like my old three speed and would like to keep it.
Joe H is running a 308 gear set, 28” tires and no overdrive behind a 250 I6. He’s getting great mileage. He’s running dual carbs in a 37, 1/2 ton. Not exactly apples to apples but has to be in the ball park with what I’m trying to accomplish.
I haven’t decided yet but I’d sure like to try some taller tires.
