ISX with DPF Partial/Intermitent Derating

Here are the symptoms,

While driving up some hills the truck slows down, like taking your foot off the gas pedal but it keeps going once clear of the hill it stays "de-rated" until shut off and limits the RPM to various RPM levels, not consistent.
The instant fuel economy readings on the little computer go from 22L per 100 Kms, to 95L per 100 Kms.
There is a smell of diesel but no leaks.
There is no smoke out of the stack, just heat.
There is no fuel in oil.
There is no engine oil loss.
The engine is not running hot.
The oil temp is not overly hot, they are always hot to me but within ISX normal ranges.
There is no blow by.
The engine runs smooth.
The regen indicator is NOT on.
There are no engine warning lights.
The engine runs smooth and idles smooth.
Fuel economy is still good, no change.
New fuel filters.
No coolant loss.
Brand new DPF filter.
New turbo.
Nothing in the fuel tanks to plug the pick up.
No "vacuum" in tanks.

When it slowed down it was not all at once, it was slowly, like taking your foot off the pedal and it was getting progressively worse and didn't matter the load.
Had me baffled because it didn't do it all the time and if you shut the engine off for 5 minutes or so it would run normally for awhile.

Diagnoses,

The increased fuel usage shown by the instant fuel economy "guage"/ indicator combined with the smell of diesel and the truck not using any more fuel than normal, led me to the idea that fuel was going past the sensor and then being bypassed from the engine back to the tanks. The hot fuel gave off the diesel odor.

There was no loping of the engine, no misses, no smoke so I figured it was not injectors.

No warning lights, so the engine is getting enough fuel pressure not to throw a code/warning light so the problem is after the fuel pump meaning the fuel pump is working just fine.

Checked to see if the fuel filters were the correct ones for the fuel used, sometimes the wrong filter is used as there is/used to be a difference between summer and winter fuel filters. Sometimes plugged or the wrong filters cause this exact type of slow down.

I checked the electrical connections, they were clean.
Checked the ground wires to the frame, sometimes they get corroded and cause weird things to happen with the ECM.

I read up on the fuel delivery system in this years 2010 ISX engine, two cams.
There are about 4 diversion solenoids within the fuel delivery system.

I had just purchased the truck so I took it to the engine manufacturer's shop and they checked it out and changed the fuel shut off valve. That appears to have corrected the de-rating but it developed a new problem of running on so I am going to take the fuel shut off valve/solenoid off and reinstall it to see if that corrects this new issue.