I understand your frustrations completely, but if I may, I would suggest holding off bringing it to a shop for a day or two while you reflect on how far you've come already. A shop will come to the same conclusions you have already; the clutch packs are working, the pump system is working, so the problem is likely in the governor assembly or the valve body. They will pressure test the circuits that have ports on the outside of the trans, and they will decide it's not worth their time to fuss with modified parts. They will have you pay to either swap in a test valve body or test governor assembly, with no guarantee on the outcome due to the nature of the modifications.
So, if you have access to a pressure gauge that will fit the ports and read high enough you should try this yourself. If not, I personally would get another valve body from a different transmission, clean it up, and try it. I know I am suggesting throwing parts at it, but it certainly has to be valve body or governor. I vote valve body since it likely had two different shift kit modifications applied to it causing unknown fluid circuit problems, as KickDown eluded to and was trying to reason out previously. Don't forget, the governor worked before you had it out; it used to shift. What really changed was the shift kit modifications.
