Running Warm

I have a 99' JGC Limited 4.7 V8 and it seems like when I have a few extra bodies or I am pulling mt 4 wheeler around, the engine temp will increase to just under red line. I power washed the cooling fins on the radiator and that did not help. My next step was to put a new thermostat in but I dont know If that is the problem either, any help would be great.