I too have tried but haven't had any luck using MCC to resolve this annoying issue with the 4th tc unlocking & the truck coasting. It looks to me like this is deeper in the transmission programming than we can access with MCC. As long as the transmission sees a minimum of 1% throttle position the converter will stay locked until it reaches the minimum unlock speed as set in MCC. But at any speed when the throttle is brought to 0 the converter unlocks & the RPM drops to idle as if the truck is coasting. then when the throttle is applied again, the converter brings everything back up to speed & the converter clutch locks back up.
When in tow/haul mode the 4th tc clutch does not act like this. It stays locked even with 0 throttle,as long as the vehicle speed is above the MCC unlock setting for the given load. just like 5th in all modes. This suggests there is something in the factory programming that is telling the converter to stay locked in Tow/haul mode but is not in the regular TCM programming??.
