2007 gtx loss of rpms and mph

[Mudnman]

There should be a flat washer on both sides of gear.if you got more money than time ,trade for a rebuilt motor.cha Ching any way you look at it.You probably have hollow valves also! If so,they break!
Special tools and parts aren't cheap.Add $80 an hour ,it adds up quick.In the end you'll be all fresh for many seasons.

 

[Sea Dood]

To add what the others said, your engine is probably toast by now. It needs to be totally disassembled and cleaned out, with new oil pumps, bearings, cam chain, etc.

Anytime you lose boost like you did, you need to shut it off immediately, because damage is done to your engine by running after ingesting the ceramic bits in your oil pumps.