Lift Install Question???
if you have a compression tester check the compression on each cylinder, and write down the readings for each one, then put like a teaspoon of oil in one of the cyls and do the compression test again, if the compression goes up higher the the original reading then its the pistons, if not then its your valves, after you rule out the piston rings as not being the problem you can do a cylinder leak down test, thats when u fill the cylinder with compressed air and listen near then head, radiator fill cap, or over flow tank for bubbles or air noise. its pretty easy if u have the tools. where are you located?