got 2004 buick rendezvous just got oil change had no problems,started over heating on way to work got really pulled over let cool down then headed back temp gage fluctuated from normal to hot depending on speed

Could be anything, start by checking the coolant level.

Check that cooling fans are working. Maybe unplugged during oil change?

First of all guys it seems to me you all keep answering the same questions with a different answer¡! Let's get real here! The Rendezvous is a nice little piece of crap! You all must work for GM so your just making them money when you tell everyone to buy some part they probably don't need! And ten more to follow. I've replaced everything you've listed and sum! Car runs good for a day or week and were back to the overheating again! Why don't they just recall this shit so we can quit screwing around here. Its a bad call by GM once again! I'm sorry but GM is where its at because of crap like this! So there's your answer. Don't waste any more money or time! Good luck to all.