Agreed with all that angelo said with the Exception of "change the tranny itself" is the AT temp light comming on as well in my experience the AT temp light will come on if its a tranny issue (slipping), but I could be mistaken but start with the basic easy stuff first. Tstat, fan clutch, ETC..are you still running the original water pump? The fins on the impeller can disintegrate if you had corrossion in the cooling system at any point in the past. Also when the work was done, did you get a Mitsu radiator or after market..just some random thoughts...Oh make sure your shroud was put back on the new Rad too.. Hope you get it worked out...maybe we can hit up Big Bear soon.