The problem with sonnax is they only sleeve valves they know give problems in the US. Here in Australia you see other issue they don't do sleeves for.
It would be cheaper to just fit a brand new GM valve body for $1100 That way you have a new unit as well as new electronics. The next problem is the Pump if you can get your hands on a new GM unit fit it also.
Im not a fan of tuning as a fix, These transmission go 100-150K with out issues and normally on original oil so tuning may clean up some problems but its not really repairing internal issues.

