I might have solved my RPM surge, 2014 1500 5.7 8HP70, surged 100-200 RPM about every 3 sec around 1500-2000rpm, until trans came up to temp then it went away. No Codes.
I first thought it might be the VVT so I replaced VVT solenoid and also new spark plugs, no change. Talked to professional mechanic friend he thought it was the torque converter not staying locked. He said if I apply slight brake that the TCM would not allow the torque converter to lock-up, well it still continued to surge even under brake, eliminating that as a cause. (I also turned off the MDS during all this).
I hade recently change to MaxLift ATF and new PPE aluminum pan before the surge started, (Maybe 4k miles ago) so I wanted to do another ATF change and see how the oil looked. Well come to find out I had refilled the transmission wrong, I leveled the transmission, not the truck, like the instructions stated (my bad). I followed the procedure correctly this time, temp not over 122, all the shifting, run 2nd gear, etc......etc....
It shifts fine and NO SURGE!!!!!!!
Can't say 100% that was the fix but, it running fine now and it's an easy check! (well relatively easy, still have to jack it up and do the procedures, but hey, if it worked for me maybe it will for you)
Good Luck hope this helps