2001 T&C with 3.3l engine runs fine, starts well, accelerates and will run at high speeds just fine, however at low to medium constant speed driving, the engine will stumble and i can feel it shaking. It starts the instant I let off the gas somewhat to maintain a constant speed, then starts the stumbling. As soon as I either let off the gas entirely or accelerate, the stumbling (shaking) will stop. I changed the plugs, and installed new wires. No codes are generated either during all of this. Could this be the EGR valve sticking?