Backfire and Won't Respond to Gas Pedal

My 2000 Dodge Grand Caravan 3.8L. 90K miles began cutting out after about ten minutes on the highway after filling up on the way to work. The car sputtered, hesitated and backfired if I tried to use the gas pedal, though it did finally catch enough at 55mph to make it to my work (about five miles later). When starting from a stop, the idle was rough and any pedal use would start to stall the van. Using little or no pedal gave me power until up to speed and then careful movement of the pedal got me to work. My computer shows no codes (code 55 repeated) and the service engine light is on. When started, the van still runs rough now and can backfire if the pedal is moved, but seems to be slighlty better (the pedal does rev the engine to high rpm while it sits in the parking lot). I did notice some small higher-pitched hum from the bottom middle or maybe further back of the vehicle at a stop a few days ago and was thinking about the fuel pump, but I cannot hear the noise now.