I have a 1988 Iroc-z Convertible and I put a 1991 350 TPI drivetrain in it(everything from cooling system to rear-end and gas tank). But the dash is out of a 1991 camaro rs and the speedometer doesn't work, the computer is reading the speed though(Auto-tap) and all the other gauges work. I have a factory manual and it says the TPI and the TBI have different signals to the speedometer. Anybody ever heard of this? How do I fix it.