I would consider fan clutch as part of cooling system, and that is not replaced, correct? A bad fan clutch could cause warmer coolant temperature or overheating. It would be nice to know the coolant temperature even your temperature gauge didn't get to HOT/HIGH. With 100+F ambient temperature...
May be get the coolant temperature when the AC is not producing cold air. I wonder if the engine is overheating.
Don't you have the factory electric fan in your 1998? Electric fan will help your AC performance at low speed or idle but I think you have some other issue since your AC is not...
Assuming you are not low in R134. I would improve the air flow going through the condenser and its cooling capability.
Clean the condenser with simple green and remove any debris
Check fan clutch performance
Check the foam is still on skid plate
It could be a clogged condenser, or other...