Last summer this car stumbled on acceleration and set code for the EGR valve. Eventually I learned that it was the Differential Pressure Feeback EGR sensor. Once that was replace it ran well for 6 months. Recently after a gas fillup it immediately began to stumble on acceleration again. This time no codes are set even though I try to make it stumble hoping to force the issue. The plugs and wires are new (as part of the troubleshooting last summer) the fuel filter is new. I even got a new DPF sensor. I've also used dry gas additives and run through about 3 tanks of gas. All to no avail. Any suggestions? Thanks.