hey, max
i sold the car to my dad and he changed alot of what you have changed, then i talked to one of my friends dads who is a GM tech and said there is probly carbon build up in the car somewhere, get on the highway and floor it a couple times, up to about 100 mph, so my dad did this and what do you know, the car made a load sputtering noise and choked out then TOOK OFF, i guess it blew the carbon out the exhaust, car has been running great ever since, i guess you can try this mabey it will work for you to, good luck,