Temperature gauge pegs, but no smoke or warning lights

Greetings,

My car just started to peg the temperature gauge after a short time of use. I though maybe it was just a sensor gone bad. I have a Verizon HUM+ plugged into the OBD port and it reports nothing. As of yesterday, it sounds like a hole developed in the exhaust. Loud! And when slowing down, it sounds like it backfires a little. I figured I would take it in to get the muffler replaced, but the temperature issue has me concerned. Can it be as simple as replacing that 19mm sensor? Thanks!