I have found it is nearly impossible to maintain a constant exhaust temp unless the terrain is perfectly flat, and where do you find that?
I will try to see what exhaust temps are while not towing on the flat. Towing my trailer, I can't keep temps under 750 degrees unless I go 50-55, and even then, going up hills the temp always clears 1000 degrees. I do notice that as soon as the truck downshifts out of 5th gear, the temps start dropping even as rpm and turbo boost goes up. Does that mean I would use less fuel on a hill in a lower gear? Even in high gear my temps don't exceed 1250 degrees unless the hill is really long. I do wish I could manually select 4th gear somehow.
Owner, Phil's Auto Clinic, Hemet, CA, 1997 Napa/ASE tech of the year
2001 D/A Crew cab long bed, Edge Juice w/Attitude Monitor, Banks Exhaust, S&B intake, BD exhaust manifold, 152k miles, 2nd set of injectors 06/25/07
2000 Powerstroke Ford Club cab short bed, Edge Juice w/Attitude Monitor, 5" exhaust, S&B intake