Originally Posted by H0USE
with the 4.30s gearing, my truck spins about 2500rpm at around 75mph,
could this harm the motor?
I get the same 2500rpm when running 75mph, with my 6.0L and the 4.30 TowBoss setup. I'm running a stock tires, which I'm assuming you're doing as well. I haven't noticed any performance issues running that speed. Fuel mileage drops to around 12mpg.