ArcticCatIV

About 1 year ago I replaced the engine in my 1989 suburban v2500 with a 5.7L tbi engine in it, I used another chevy 350 from summit racing and used most of the old Accesory drive then, about 6 months after I completed the build it noticed a loud rattling noise that sounded like detonation to me but only under low speed acceleration and it would stop when I let my foot off the gas, so I began troubleshooting the issue. I replaced the egr valve, put colder spark plugs in it, replaced the knock sensor, tried high octane fuel, retarded the timing adjusted the valve lash and now I am lost, the noise only gets worse the more I drive it. Any Ideas?