After Provent and SEGR+GDE tune the sensor is clear. Well, I last checked it 15,000 miles ago and it was clear. 10,000 miles before that it was clear, 6,000 miles before that it was clear...
I think the EGR being dead + the Provent pretty much fixes it.
As for the dragging, you may find RPM has more to do with it than speed. Are you running the original muffler? Back in day several complained that it was restrictive and that it acted like a engine break when they took their foot off the go pedal. (Edited: Opps, I see you have straight piped it).
Also, if you are on the stock tune, see here. Turns out the ECM tune helps with this, not the TCM tune:
http://www.greendieselengineering.com/f ... st/10.page