Just got back from a trip to the dunes with the toyhauler - would guestimate the weight of the 5er was right arouned 11-12k when towing.

After driving for about 4-5 hours running strong at around 68-70mph (getting 8.5mpg :-() we were going up a steady grade and the truck started to buck a bit. The motor seemed to be surging like it would react if it had a clogged fuel filter.
The RPM's were right about 2k or a little over - it did this about 4-5 times on the way to the dunes and about 6-7 times on the way back.

I know it wasn't wrong fuel - only used Ultra Low sulfur; had the truck re=programed on the 15th of Aug.

Anyone ever heard of this? The truck would just start bucking and and such - to get it to stop I only had to let off the accellerator???

I love my new truck but this one has me baffled. The MPG sucks - but I am hopeful it will get better once some chips come out and we don't have to push the motors so hard to get the power out of them.. (that is what helped my old Duramax).

Any ideas guys?

 

My guess would be that the PCM entered a regen cycle. A similar thing happened to me while cruising at highway speeds. The onset of the regen felt like I hit something in the road and then began to slowly "surge". The surge was actually negative going from normal to a slight loss of power. The negative bump in power is what made me feel like I hit something in the road. Does that sound like what you experienced?

 

I wouldn't think so, I did hit a regen at the dump station before going home - it happened after that also. I wouldn't think I would be in a regen - then out of regen - then go into a FULL regen cycle - then have the same symptom. Never know with this Regen stuff though. It was pretty much "bucking" - not a little loss in power but a full blown on off on off on off on off on off until I let off the accellerator.
The temp outside was pretty warm 89 degrees or so.

I am taking it in for a reprogram tomorrow on the newest TSB (I think it already has that program in it but I cannot tell as I am not the Ford tech)

I should know more tomorrow and I will post up.

It really seems to be a programming issue - maybe like the computer was reducing fueling so the tranny could shift or something but because I was in tow/haul mode it was holding the gear?

Maybe the new program that they put in it was the culprit? It is supposed to fix the gear hunting and allow it to hold longer - maybe that is the situation - maybe the fueling and such wasn't properly adjusted to match?

Dunno. My friend is a service manager and he said that when the truck is hooked up; they automatically get downloaded with the newest program from FORD. Anyone know if this is correct or just his "spiel"?