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Thanks - that really sounds like the problem - obviously they are not looking in the right direction!!!!
Some of the throttle/injector problems can be caused by overfilling the oil. If they put more than 13.5 quarts of oil in at oil change, the crank will beat the oil to foam. Then the foam won't work the hydraulic parts such as the VGT(turbo) valve and injectors.
The dip stick is not reliable as Tim Lampkin has proven by measuring every dip stick in Albuquerque and finding them all different.
If you don't fill it past the add mark you should be OK
This sounds crazy but do a search on oil level on this forum and you will find that several have solved their problems by lowering the oil level.
The dealers are on the right track when they figure out the oil is the problem and start trying different viscosity. The excessive level is likely the problem.