RPMs wavering/fluctuating

Hey guys. I have a 2011 Malibu LS. The problem I'm having isn't limited to Malibus as I have seen a discussion that went unresolved on a Pontiac Grand Prix. Sometimes when I'm going 30-50mph and then try accelerating further, the car's RPMs will go back and forth between about 2000-2400. It seems like it does it more when it's really warm outside (I live in Dallas), it didn't do it at all this past winter and now it's starting again. Also, I have seen my temperature gauge go crazy. It maxed out and then dipped low and went back to normal. The Pontiac post mentioned that as well so I thought it must be related. I'll answer any additional questions you may have. Thanks for any help!