help w/2001 4.2l

I have NO POWER...fuel press good, no exh. restriction, no check eng lite, have checked/replaced: MAF, DPFE, knock, egr, cps, O2, ....Anyone have any ideas why this thing won't get out of it's own way??? The exhaust manifolds can get RED!!! but there's no restriction in the exhaust... Can it be a bad cps even though it tested OK????? timing goes to -27 when flooring it in neutral, then as it reves, comes back...seems to rev OK not under load...once under load...forget it!!!! no guts....
any help would be appreciated.....