Compression check is quick, simple and easy. If the numbers are low a new cam will not correct that. A leak down test can zero in on weaknesses. These are not high comp. engines in stock form, less than 8to1 I believe. Increasing that factory ratio helps to wake them up, but requires, expensive pistons or head shaving or a combination of both.
I recently paid over $500 to have a 302 head cleaned, magnafluxed,surfaced
guides replaced, seats ground, and stainless valves supplied.
P.S. I see you are already posting on the GMC site
