1995 Monte Carlo Z34
#1

I have a 1995 Chev Monte Carlo Z34 with 163000 km (100 000 miles). I just noticed the other day that while in park, if I rev the engine, once it hits about 4000rpm, it starts to chug. I took it out on the highway for a snort and had no problems. At a red light I put it in neutral and revved it with no problems, and then tried park and it happened again. Would anyone have any clue as to why it is doing this? I would appreciate any help as I am trying to sell. Thanks very much.
