bad lugging problem

This just started friday morning when I was going to work I noticed that the car was lugging(it was shaking things bad enough to rattle interior trim) pretty bad in OD going down the road. I took it on a road trip over the weekend and again noticed it going down the highway. it seems to happen only in OD going down the road between 55-65 with the stall locked ~1500-~1800rpm. Any light acceleration or hill climbing makes it worse. I was thinking that maybe its time to put new plugs in but I've only got about 2000 miles on it. Only other thing I thought of was maybe the trans mount let go. Guys got any ideas?

I have had this happen and the driveline was unbalanced. Hope this helps.

Sent from my SM-N915V using Tapatalk

If the trans mount was gone you'd know in every gear especially pulling away or rolling to a stop when it bites 1st gear. I'd think more of a drive train imbalance

Torque converter clutch not staying locked. Possibly slipping or some type of electronic or pressure issue. That's what it sounds like since it only does it at those speeds. That would be myguess

I'm hoping its not a trans or stall issue. I highly doubt its a drivetrain imbalance since it just reared its head after 2000 miles. You would think that if that was the issue I would have had it since the engine/trans was put in

I think I may have found my issue... got a little oil on this spark plug... #7

Attachment 33634