ok here's the history of this car. it sat not working for like 2 or 3 years. then my friend bought it not running and it needed replaced head gaskets because water got into the cylendars. he got the work done at the mechanic for $800 (pretty good deal i think...) then he got it home and i had several other problems. it idled at 2,200 rpms, shifted into gears really hard. it wouldn't down shift like the electric auto didn't work or wasn't tuned right so he took it to a chevy dealer and had their shop re-tune it to stock settings and everything worked right (after replacing the TPS) idles right and everything. but now when you're stepping on it, when going from 1st to 2nd gear it goes all the way up to almost 6,000 rpms and then a loud pop and then it shifts into 2nd gear. what's the problem? is it tranny trouble? engine backfire? or is the ECU just not reading everything correct yet and driving on it a few miles will set it all straight?

 

Try the drivetrain section. Someone there will most likely know more. Maybe a Mod will be nice and move this post for ya.