1991 Lumina 3.1 engine, I R&R the throttle body so that I could put a new gasket and o ring on the cap with?

the oil drive gear on it that goes into the hole where the distributor is suppose to be. I also removed and cleaned the EGR vavle. The main port hole in the plenum was 90% plugged. I then took the car 8 miles on the eway and then parked it for 1.5hrs. On my way home the car started chugging at 70mph and then went down to 60 then 50 and when I exited it stalled at the light. It then stalled 5 more times before I got home. What could I have done wrong or is this a coincedence.