1999 Dodge Durango

Our durango backfires while we are driving down the road we have replaced the spark-plugs and the wires and it was still doing it so we had the cap and roter fixed. Now someone said the the head gaskets need fixed but I dont think that is the problem . I think it is in the electrical system somewhere. Could it be the battery it registers somewhere a little bit before the middle marker one time then another time it will be a little bit on the other side of the middle marker. Maybe it is the battery wires? . Maybe. I need your input my husband is threatening that he is going to take it back and throw the keys at the dealership.
Kimberly Lynch
May 6, 2013.

I would start with basics. Compression test is the start. It could be a bad cylinder.

I doubt it is the head gaskets.