When you say "first generation" atlas Geep, surely you don't mean the ancient red geared Roco drive? There's not much you can do to improve that...
As a modification on the Beardonizing, I take the inner bearing block off, then ream it out a little. I've found that you need to relieve whatever tension might be in there, but you still need it in place as a spacer to keep the worm gear stable.
It could also be something as simple as the motor not being seated in its housing all the way. Any little shift in the drive line will make problems.
Lee
