2005 Ford Taurus Question: Car surges all the time. Upon take off, speeding up or inclines.

Sounds like cat is going bad and plugging up. The backfire could be pressure building up due to this issue and blowing out the flexpipe which will need replaced. Good way to check is to get your car up to operating temp. and put your hand about 3 to 4 inches behind exhaust pipe. If flow is restricted, the exhaust flow will be decreased and will be much hotter than it should be. If you have to move your hand because of the heat, it is too hot and cat. will need replaced. Also, check flexpipe for holes or breaks. When you are sitting at a light, the stronger smell of exhaust fumes will also tell of a break in the system near the engine in the area of the catalytic converter or flexpipe.