Hey guys, im totally stumped on this one. Started noticing my grand Cherokee over heating when I get the RPMs up around 3000 to 4000 and when I climb a hill. Looked over engine and no leakes, oil isnt colored and no other signs. Start with trouble shooting parts. Replaced cap, then water pump, then radiator, then radiator fan. Did thermostat a while back but dont think it would be bad after about 10K miles. Im stumped to what it could be? When driving and when it starts to overheat ill get off the gass and crank the heat on high. The temps come down to normal but will rise again when I climb or rev back up. Any help is appreciated. Thanks all in advance.