1996 Chevy Lumina engine light/ RPM double/ sort of grease

I have recently had the engine overheated found out
maybe cause a leaking radiator, I replaced it then replace rear manifold was split in two I don't know
what caused it, I replace the egr tube there was a sort of grease like on it and on the egr, and ont in-take also. I replaced the oxgn sensors the year before I had replaced the spark plugs and wires, I replaced the fans
relays I can only see that one works only with the a/c or
without. The engine overheats when sitting stationary and when you hit the gas pedal the rpm doubles when speed at 20mph the rpm is of 40 or 50mph and it is going slower than that and slower at taking off. Any info on all of this.