My Ford Focus '01 has been doing the classic hesitation and stumbling motion when it is going along at a constant speed. It's very noticeable at 45mph. I have an automatic transmission. I took it into the shop and they ran a diagnostic and it came up as insufficient EGR flow. I had read FocusHacks.com and I was trying to explain to them that this is a problem on the Focus and they said that everything was ok and turned off the CEL. Within hours the CEL came back on when it was doing the hesitation and stumbling at 45mph. So can I assume it's a problem with the DPFE sensor and that should be replaced or should the EGR valve be replaced?