https://www.amazon.com/Range-Technology-Active-Management-Disable/dp/B00BR1R8N8
Have a 2007 silverado z71 that I purchased at 67k miles. First thing I noticed was the truck was burning oil. Bought the range tech AFM disabler and it was the best purchase I have made on this truck. Completely fixed the burning oil problem and the shifting and throttle response is much better.
I love my 2011. First thing I can't recommend enough is disabling AFM with an OBD2 device, like this to avoid engine issues in the future.
Is there anything plugged into the OBD port? Like this: Range Technology Active Fuel Management Disable Device (Blue) https://www.amazon.com/dp/B00BR1R8N8/ref=cm_sw_r_cp_api_i_R79YYMEGYZYPC4AN7E3R
I bought an 07 about 8 months ago after having a ranger for 5 years its awesome...Here it is after Installed the RC leveling kit ...may I suggest that you pick up the range Active Fuel Management disable module it keeps it out of v4 mode and saves your engine in the long run ..you get a little worse mpg but its better for it