i recently did a sas on my 90 pickup with 5.29 gears and 33's soon to be 35's. and my speedometer is way off! on the fwy it says 80 but im going like 67! i used my gps and i even found speed traps on the streets! and its says 55 on my speedometer and 45 on my gps/and speedtraps! is there a way i can fix this? or am i screwed.