overheating

hi, i am having issues with my 2001 mitsubishi montero sport 3.0. It keeps overheating and i cant seem to find the solution. i have already replaced the thermostat, fan clutch , and radiator, it still keeps overheating. I feel like im getting suckered by my mechanic because i have gone back 4 times in the past 2 weeks. Changed my thermostat, came back 2 days later, he told me the fan clutch , so i had it replaced, came back about 3 days later, then i personally found that my radiator was broken so i had him change that, and again came back about 3-4 days later. if he has looked at my car and also did the computer diagnostics to it twice, shouldnt the problem be fixed. I told him about my water pump but he said he checked it and it was good. Any suggestions from anyone....this guys is really making me frustrated....i would have just taken it to pep boys if i wanted to get screwed...they will charge an arm and a leg but at least i know the problem will be fixed