Well, IIRC the ZZP kit is just that- a shift kit that you can install to adjust the shift points and harshness of engagement. I think the one from Trans-go is just used to improve failing parts and keep the shift points where the ECU wants to see them thus reducing/eliminating the P1811 issue. I had this code on my 00 GT and installed just the new accumulators and whatnot from the TransGo kit from Dave at tripleedgeperformance.com and the trans hasn't shifted hard or set any codes since that time, and it's a high mileage trans at that. It does shift a bit more firm but it's never going to bark the tires, which is a good thing. Your call I guess.
Transgo SK4T65E Shift Kit This is the kit I bought/used.
