To rakel i am still not sure where the egr valve is? or where the DPFE sensor located?

there is a tube just behind the alternator with looks like an EGR with one va line on it. the code i recieved was P0401 EGR flow insuficient detected. would that mean it is plugged? the engine chugs when you step on the gas. as if you were learning to drive a stick for the first time but mine is an automatic and it has never done that before. we just pulled a 6000LB. trailer 500 miles and then it just started happening.