I'll tell you my opinion on that and you can take it for whatever it is worth to you. Just keep in mind that these are my thoughts, my opinion, my experience, etc.
Ive checked with tranny shops when my tranny started acting up and some of them would just rebuild it and get it out, others said they could do 'performance' upgrades, but could not tell me a lot about what they would do. A couple seemed to be able to speak intelligently about 'performance upgrades' but it was like a blanket upgrade, not something specific to my goals and intentions and didnt always give me confidence they knew why a performance upgrade was needed.
The point to this and what I learned is that you can probably find someone that can rebuild it locally and may even do a good job. What you will be hard pressed to find, outside of someone like Trannyman is a shop or repair person that specializes or is as intimately familiar with the 4T65E and can speak to you about it on all levels. It would be worth the money to me even if he were more expensive.
