As my mid-nineties GMC vehicle will likely be surpassing the 500,000 mile mark this summer, I decided it was time to do a compression check of the engine cylinders (5.0 L). With a brand new compression gauge, all the cylinders read approximately 180 psi. Knock on wood and all, but I have never even replaced so much as a gasket on the motor. Yea, I know! Right?