wms2742

I have a 2015 Chevy Silverardo 2500HD that is about a year old with 14k miles. Since it was a couple of months old it developed a drivetrain vibration, between 30 and 50 MPH. Between these speeds everything is fine until you apply a slight acceleration to the gas, usually when going up a slight grade, the vehicle has a significant vibration in the drivetrain. If you let off the gas, it stops. If you increase the gas until it downshifts, it stops. No vibrations of any kind at faster or slower speeds outside this range. I have had it to the dealer several times over the past 6 months. Each time they have acknowledged the problem. First they thought it was a tire out of balance- Did not fix the problem Then they put it on a lift and took the driveshaft off and claimed the vibration stopped so they rotated the driveshaft 180 degrees and re-installed- Did not fix the problem Then they claimed the drive shaft was defective and ordered a new one- Did not fix the problem. Today they had thier "transmission guy" test drive it and he determined that it is a know issue GM has with the Fuel Management System and the Cylinder Deactivation System. GM knows about the problem, but to date does not have a fix, and there is nothing they can do to help me. I questioned the Service Manager that I didn't think the 6.0L even had cylinder deactivation (thats a 1500 feature) and he asurred me it did and there is a reading next to the odometer that tells me how many cylinders the engine in running on. When I asked him to show me the indicator he jumped in the truck and said "huh it should be right there", then said "well thats what the mechanic told me". Anybody had or heard of this issue? Anybody know if a 2015 6.0L has cylinder deactivation? Any suggestions are appreciated...