I have a '92 GXE w/ 210K miles.... I have had damn near everything replaced except the motor and transmission. My car is running hot and I have a new radiator, two new cooling fans, etc. So I am pretty sure it is my thermostat. My question is:

When changing the thermostat, are there some dos/don'ts that I need to beware of? Like making sure I do xyz... Or making sure I don't forget to do xyz?

now.. to the transmission....

When I am accelerating and I get to about 2,000 rpm, there is a strong vibrating noise in the engine. I originally thought it was my motor mounts, but after replacing all of them, I still have the vibrating noise. And it is getting worse. Is this a sign that my transmission is going bad?

thanks!