My temp runs about the same, just above half in traffic and just below half on the open road. As for the backfire............no clue. But ask yourself a couple of questions and this should narrow it down.

1) Does it backfire thru the exhaust or thru the intake ?
2) Does it backfire on acceleration or after you accelerate and let off the gas ?
3) Is it a single detonation or several intermediate low volume "pops" ?

These are questions the dealer will ask (or should ask) if you bring it in to have this checked out.

Just my Dos Centavos !