thanks all! i think you are right about the batteries. I recharged the batts and ran the truck with batts hot off the press. cogging almost went away. however, things got progressively worse as batts drained. looks like i may need lipo, but a little too much $$ for me to spend now. i'll try and gear down to see if it helps.
I had a very similar setup and I think that gearing down will help alot, maybe a 13 or 14t pinion would be better. Those batteries may have some issues moving the truck around properly with taller gearing.