are your looking for suspension /'better ride" or looking for more power??
better ride= swap in a mono rear skid, or another brand skidframe
more power=clutch kit
The stock exhaust is good and the sled makes decent power, the clutching is the biggest bang for the buck if its power you seek and it doesnt kill the gas mpg, aftermarket pipes eat gas like crazy.
rear suspension is lacking as the pro action is pretty outdated today, but the front suspension still works decent and the slot car type handling of the trailing arm is still a desire, so you need to go with a differnt rear skid if you ride in the bumps alot.