So I have a 2007 3500 mega cab 4wd. I have added a 4" no cat mbrp exhaust, AFE stage 2 intake and a edge evolution cts always in tow mode. The truck has 116,000 miles on it and 3.73 gears with 35" tires. I regularly pull a 40' toy hauler with my race car in it that weighs in about 15000 lbs.The trans started slipping in second and I adjusted the band, changed out the governor solenoid to borg warner, changed transducer and speed sensor. It was fine for a while and now it is slipping again.I am out of adjustment so it's time for a rebuild. Here is what I am thinking please give me your advice on what I should or not do. Thanks for the help. Also let me know if I am over looking anything.

PATC Mega viper kit
Alto master rebuild kit with all Red Eagle clutches,
direct Power Pack and all Kolene steels,
Carbon flex band
Transgo 48RE Shift Kit.
Sonnax oversize band apply servo
leak free accumulator piston,
unbreakable Power Wedge.

---Add ons after the kit---

Triple Clutch Billet Converter with a Billet Apply Piston w/billet stator
SONNAX low / reverse servo
Heavy duty strut for 2nd gear band
Overdrive Unit Bearing Shim / Case Saver
Extreme Duty Hard input shaft

 

Did I miss flex plate? 15k is not huge but somewhere very close I would start thinking billet output. Hard OD shifts, locked up can reek havoc on outputs. Weight or boosted launches kill output shafts.