me and a friend done some hardcore driving today and when i got home i was sitting in my car letting it idle for a few minutes and a lot of smoke was coming out where the shifter is... what could this be??? its a 88 GTU with 158,000 miles...

 

You could have rattled some bolts near the cat loose which might have caused the exhaust to not be sealing well anymore. That is the first thing that comes to mind.

 

Maybe an oil leak at the transmission extension housing rear oil seal.
Put it on a lift or jack stands & look underneath.