Vibration between 1500, and 2k RPM

I have a 2018 TRD Off Road with 75k miles on it now. I have Michelin Defender tires, (only about 10k miles on them) Ive been dealing with this annoyance for a long time, and I just can't figure out why its happening. I'll be driving down the road and the truck will naturally coast around 1500 to 2000 RPM. not while accelerating just at coast. I will feel a vibration that feels like the engine is stumbling. Like its about to die. that being said the RPM doesn't fluctuate at all, and the exhaust sounds normal. from everything I can tell its running like a champ.
Things I've done to fix:
1. replaced spark plugs, (with OEM Densos)
2. Got the OTT tune (highly recommend)
3. Got great highway tires (Michelin Defenders)
4. Flushed the transmission
5. Flushed front and rear Differential and Transfer case.

aside from the vibration situation the Truck runs perfect, I get pretty good fuel economy and the truck makes great power now that I have the OTT tune. Any suggestions on what it could be?