At my wits end...HELP!!!

[Mr 5 0]

Unfortunately, it sounds like you have a leaking (blown) head gasket.

You can get a good idea just by hooking up a simple vacuum gauge to a hose that goes directly into the intake manifold. A quick and dirty method is to use the MAP sensor connection (T-fitting required) or use the PCV hose (but it may affect your idle).

Any big fluctuation in pressure (10" hg) probably indicates a blown head gasket (or a dead cylinder) which would explain your overheating problems despite all the fixes you've already tried.