96 Aerostar Cooling system problem

This particular van overheats when A/C s on. T-stat s been replaced, w/pump was replaced 25k miles ago. I've checked the following and everything s checked out ok; fan, fan clutch, belt tensioner, coolant level, radiator and condensor for any airflow restrictions. Any other ideas of what thhe problem could be would help. I 'm thinking of replacing T-stat again with one that opens sooner. Thanks in advance.

by the way its a 3.0, RWD, with no rear a/c