WHAT !!!! ?????
Nobody said anything about a filter kit.....
1. If it only slips occasionally going into 3rd gear, you may just need a band adjustment .......which simply entails tightening an adjustment screw. It the adjustment screw will not "torque" up to specs, then BrooklynBay is right.....it is broken.
2. Or, it may just be the electronic pressure control sensor per the DTC Trouble codes.
***If it occasionally shifts into third correctly..........your intermediate band is not broken.
Attack your problem in that order if you have to start somewhere.
After checking the intermediate band, I'd certainly try replacing 1 sensor (new), before I replaced a whole block of "used" sensors bought off of e-bay. My God ! ! !