when I reverse with my 00 TL,as soon as I let go the throtle there's a clunking noise coming from underneath,are the mounts finished?

more likely the mounts are shot. Have someone do the reverse, while you watch under the hood and see if the engine have excess movement.

There are 5 mounts between engine and transmission
If you not sure- have a shop check them for you
It gets expensive to randomly replace things