I have a bone stock 2006 Dodge Ram 2500 Mega cab with the 5.9 Turbo Diesel. I purchased in 2006 and know every repair that has been made to the truck (which I might add were mostly Dodge repairs as the Cummins has thus far been bullet proof). 170,000 mostly daily driver miles with maybe 6, 160 mile round trips a year pulling a 26' camper. My question centers around the following: Within the last 500 miles I have noticed that when decelerating (say foot off the throttle), that the engine no longer just gracefully backs down to its 700 +/- idle RPM's. It now steps down, say from 1800 rpms to 1500 rpms, then to 1200 rpms then to 900 rpms then to idle of 700 rpms.

For comparison, my neighbor has same truck but extended cab and today while running in park we tested his and his went from 1800 rpm straight down to 700 rpms like mine used to do. Has anybody seen this before and know what parts is failing? By the way, there are only two codes set with one being the oil pressure sending unit and the other something to do with a security module. No codes pertaining to TPS/APPS.

I have removed the ground cables from batteries for an hour and problem continues, Even erased the codes with my Actron reader and no change. I have further followed the steps to re calibrate the TPS/APPS with no change.
And if the consensus might be that it's the TPS/APPS, do you really need to purchase the entire accelerator pedal assy. to install a new TPS/APPS?

Hope I have explained properly. Thank you.
Garry.