Sounds like you have the 4.11 gear, what is causing the main problem with the speedometer/lack of speed issue are the tires. 235/60/15 are much smaller in diameter than the oem tire (26" vs 29"). That will cause the speedo to read off, plus limit the top end, as the shorter tire will be the same as if you put a lower gear ratio in the differential. To improve the speed issue, there is a 3.55 gearset available from Patrick's, or you could go with a taller tire.
cool, thanks for the speedy response.
i've been scouring the books and i can't find the OEM tire size, though..
http://chevy.oldcarmanualproject.com/chevyresto/53155.htm not sure what measurements they're taking there
EDIT: nevermind, i guess 6.5 is 6.5inch width with a 100% aspect ratio.. so my 235/60s are 2 inches shorter..!
