The best place I have used has been RC Trans & Gear.
Randy [the owner] has been great to work with on projects I did not have the time for. Probably one of the most honest people I have met.
I was having 4WD issues recently. I dropped the truck off with the encoder motor in a box [a new one and the original] and he looked at it and did a diagnosis. It was electrical related [as the new Korean Dorman encoder motor was defective!].
Randy didn't charge me a cent even after he spent the time to look at it. I also had him and his shop do some work on my 1971 LeMans with great results...and a few years prior he did some work on my brothers old GMC Typhoon.
Hands down a great shop and person to deal with.
The cool part of his shop is that he has posters and articles from old muscle and random projects he worked on, really neat!http://rctransandgear.com/