No reason to change gearing in a Turbo Buick powered car TTA or GN especially at the performance level you want. Throwing good money after bad. Unless you do a full on performance build you will not see high rpm out of a turbo v6
K&N / cold air induction
If you have a stock...
BAER Brakes 1LE upgrade kit. Drilled and slotted rotors, performance pads, Braided Hose kit $750 shipped CONUS
2004r Aluminium trans pan $240 shipped conus
Heditis subframe connectors ,Tubular rear lower control arms and panhard bar. Sold
TTA APR head bolt kit $48 shipped us
While I agree with not stirring up things in sales posts, you did open yourself up with the diatribe on the spoiler rather than just saying it was a stock one for sale. I did not see anyone posting anything before your original vent.
Oh my gosh a Buick that leaks oil, the hell you say. Just kidding. It is usually rear intake or valve cover if its coming from above the starter. Every once in awhile a bad pcv gasket can cause it to but you will usually see that looking from above at the rear intake. Rear main seal easiest...
I can't vouch for them but might be a place to start. Tta Performance - Turbo 4.9 301, PEVR rebuilding, Performance Parts Also if you don't belong try the PY forums 77-81 Firebird & Trans Am TECH - PY Online Forums
Not saying this is your problem but we chase a similar problem for a couple of months until the drivers in the computer finally went out. I would check what Robert said above first but if you cannot find anything else try to borrow a know good computer.