StevenB L98/LS1

1991 trans am 5.7 TPI. im having trouble trying to understand why my car is idling high, or fluctuating when its being stubborn at high rpm.

okay so i took the car to the shop yesterday where they installed my tps back in january saying if it was bad they would replace for free. so i went there today and found out they tested it and it was good. okay now that tps is fine, i cant understand why im getting a high idle then. idle screw has never been touched, new distributor in the car that solved my idle surging and dying problem back in november. it drove fine for 5 months jan- middle may, accept the egr which i just found out a few days ago what the problem was, and im trying to track down the part. i cant believe its discontinued. but ive always had to get the egr replaced, i always held off though for some reason.

But any thoughts? i mean for some reason when its not idling right and idling at 700 or 800 rpm and it effects the shifting. the shifting sucks *** majorly, it slips out of overdrive when i barely push the pedal down any just to gain some speed and it just keeps slipping. when its idling perfect at 600 and driving fine, it shifts just fine and stays in over drive? Whats causing this? The only answer i got was from my machanic today saying btw i do have a small radiator leak now i have to replace, and he said a cooling sensor when its malfunctioning cant cause everything else to mess up. im still not understanding what it could be though? i replaced the damn coolant temp sensor already, o coarse being stupid last yr i had to buy one from an autozone instead of oreailys or advanced. But it seems to work fine though. Well i hope someone can help, because im out of ideas right now.