soloboss

Hmmm - I'll go on the presumption that the problem is not electronic. Nick gave you a tip to figure that one out using a voltmeter and checking the motor voltage pins.

Let's go back to the slick table top so you can demonstrate the rotation without actually flying and damaging the helicopter. First thing in my mind it blade tracking. The upper blades are set using the link connected to the flybar. Unless the blades are warped, the upper tracking can be set perfectly. If not perfect, boil the blades to allow them to reshape to original condition.
The bottom rotor do not adjust. If the tracking is not 95% perfect, remove them and try other blades looking for the perfect balance and tracking. Or boil them so they return to original shape.
And check tracking at a high enough rpm that the heli is lifting to the point of almost flying. If you have tracking issues you will have flight issues. Don't give up until tracking is right.

At this juncture, tracking is not NOT the problem.

Not good yet? Remove all the stuff from the upper and lower rotors - blades & flybar. Now spin up just the inner shaft and listen to it. Do the same for just the outer and listen to it. Do they sound the same? Is your gear mesh equal? Don't hold the motor at max rpm because it does go over speed, but goose the inner, then the outer shafts and listen to them slow down. Do they coast about the same length of time? These tests should find any binding or drag. If you have drag, remove the drive gears from the motors and goose the motors again, listening for a difference in rpm and the time required to coast to a stop.

Some have had the screws from the lower blade hub tightened so tightly that they contact the inner shaft. IF you remove the inner shaft and look through the outer shaft you should see more than enough room for the inner shaft to pass through with no drag. The correct screws used to secure the lower head to the outer shaft will not engage deeply enough to contact the inner shaft. If you see the end of a screw when you look through the inner shaft, you may have the wrong screws installed from the factory. Not likely, but we're looking for something that is not likely.

Do you have any vibration in the helicopter? If something is shaking it will certainly throw the flybar out of whack and that will mess up the upper rotor drag and cause TBE and rotational issues. If it shakes, start removing stuff and running up the rpm until you find out what makes it shake. Fix that.

Is your battery balanced? Is it balanced under load? If you have another battery, try that. OK, so if you had another battery, you would have already tried that. Sorry, Your point.

The proportional pot and the Tx trims work in harmony. You should be able to get close with the pot, and then dial it in with the trim. I always charge the pack, run it for a minute, then set the pot for stable hover with the trims centered.

Maybe something in here will lead you to the answer. Tough issue. Keep us posted as you work through ideas.
We're with you - Soloboss