Can't get my FMS Skytrainer 185 55" to taxi & roll for take off straight!#

[Herndon Flyer]

FMS Skytraner 55" 185 will not taxi straight!# I've had four of these models and the last thee(3) developed a nestling issue, to turn drastically to either side, that it is awful. I installed a stabilizer and gave the yaw as much authority as possible and it worked great for a long time until gravity claimed it during flight; I goofed, crashed nose first. It was fixed, the stabalizes seemed to be working and the problem started again; the only way I've been able to mitigate it is by taking off "balls to the wall" and get up off the grouund ASAP. However, when I land it rolls BEAUTIFULLY, the moment I touch the rudder to turn it stats's again. I've checked all the links to make sure the isn't too much play, I had to replace the rudder servo with a 17mg metal gear since the local hobby shop did not have 9mg metal gear servos. The push/pull rod is securely fasten to the sides of the fuselage in a plastic enclosure; I've replaced the nonse landing gear with the linkage and even put one size bigger screw to secure linkage to the upper landing gear's main shaft AND checked that the suspension's linkage to lower shaft does not have play, which it does not. I also went to the extent of checking the play of the wheel and put bearing grease. Lastly, I reduced the authority on the stabilize's yaw setting and still have the issues; HELP BEFORE I LOOSE MOE HAIR & I'm already bald! I like this model & I like scale flight; any constructive serious suggestions are welcome. THANK YOU!

[xviper]

Have your tried using lower rates and higher expo? Your plane has a tricycle gear where the wheelbase is quite short. This lends to a twitchy steering on the ground. Also, check where you've placed the battery (ie, is your balance point where it's supposed to be?) Tail heaviness or even too much nose heaviness can contribute to twitchy steering.
Also, what kind of ground do you fly off? Grass can be a bit of a handful and the need to power up and get off the ground quickly becomes more needed. If it's happening on a smooth runway, then a slower run up with "dumbed down" rudder input may be needed.