If you have read any of my previous threads you will see I recently converted an old TMS to electric. It flys great, the rudder and ailerons trim out to center, but on taxi it turns sharp right and even with full left rudder I can't go straight.
For tail draggers, make sure that you have a bit of toe-in on the wheels. Any toe-out will almost guarantee a bad taxi experience.
The late Bill Skipper, full-scale air show pilot, RC enthusiast, and RC Report magazine columnist strongly advocated toe-out on conventional gear planes.
I have had toe out on my taildraggers since about the mid-nineties and have no problem taxiing.
A flyin' buddy had a Great Planes .20 size J-3 cub that was a ground looping fool until I bent in a smidge of toe-out. Toe-in usually works too, but on that airplane the toe-out cured the ground looping tendency.
It would take a shed load of right thrust to make a plane turn right even when applying full left rudder.
On a plane like the Telemaster you should have around 3 degrees of right thrust, give or take. Unless you have MUCH more than that I dont think it could explain your issues as described.
Another theory I have is that my little 46 oz/in servo is stalling out not able to overcome the tail wheel. I ordered a 130 oz in that fits the same footprint.