94 lumina 3.1 overheating

alright i got a 94 lumina euro 3.1 the problem i have is that it keeps over heating, but the catch is it doesnt over heat when your driving only when you in traffic or stopped for 10-15 minutes, the tricky part now is we have had the thermostat changed that wasnt the problem, next the water pump replaced that wasnt the problem, then we finally moved onto the coolant temperature sensor thinking its sensing the temperature wrong but nope still not the problem the only thing left i can think of is the radiator, but it looks like it is totally fine no dings anywhere or anything of that sort like rusting it just seems that when you give it gas it pushed the coolant through and cools the engine but when its sitting there idling it doesnt have that flow and starts to heat up, if anyone has any suggestions on what it might be besides the radiator please let me know thanks .

Do your radiator fans work? Only 1 should operate once the coolant reaches operating temp. Both should turn on when the a/c is used. If the fans don't work, you won't necessarily overheat while driving as the air is being forced through the radiator, but when stopped (idle or traffic) the air doesn't rush past to cool the antifreeze and your temps go up.

yes fortunately they both do work and come on when needed and a/c fan turns on with ac so thats not the problem thanks though