Troy-
Sounds like you have a way higher rear gear than a 2.56
My '67 has a Turbo 350 and a 3.73 rear end ration.
At 70 mph I turn about 3100 RPM. Way too high for
today's gas prices.
My plan is to install a 700R4 overdrive which will bring the cruising RPM down to 2100. That is in the range my '95 Silverado had and it had excellent power and mileage.
Here is an excellent link to help you decide on gearing and so forth. It accounts for tire size, tranny and all the variables.
http://www.classictruckshop.com/garage/shopmathgearcombo1.asp Good Luck!
_________________
Guy
_________________
'67 C-10 283/350
