I'm posting this from a private message so it may help other machine owners. Darin, Sorry for the late response. I hadn't noticed a message from you. What are your machine serial numbers? On the TS14D or DII, the failure of the torque converter lockup won't affect the transfer of power thru the transmission. The lockup feature only engages in gears 2-6 when the slip thru the torque converter is minimal. Like driving across the jobsite at high rpm and the engines really aren't working hard. The purpose of the lockup is to reduce the heat generated by the oil in the torque converter. If the power flow thru the transmission is interrupted during torque converter lockup, something else is happening. Now, if power is disrupted during lockup, my first thought, all the transmission solenoids, and TCU share the same ground, next to the batteries. If that ground is compromised to flow full current with three solenoids powered, the problem spot will drop the voltage low enough to drop out the two clutch pack solenoids, interrupting power flow. The Transmission Control Units(TCU), one for the front transmission, one for the rear, are located behind the hinged kick panel at the cab step. Make sure the ground ring terminals are clean and the chassis lug is clean. Spray with battery terminal protectant after reassembly. On the TS14G, I question if you are only having problems in 4th and 5th gears at the rear transmission. 4th gear uses clutch packs 2 and C. If clutch pack/solenoid 2 had problems, you'll see the problem in gears 2, 4 and 6. If clutch pack/solenoid C had problems, you'll see problems in gear 3 and 4. 5th gear uses clutch packs 1 and B. If clutch pack/solenoid 1 had problems, you'll see problems in gears 1, 3, 5. If clutch pack B has problems, you'll see problems in gears 5 and 6. If you have skinned up, broken wires for any of those clutch packs/solenoids (power and ground- each solenoid has individual power and ground wires in the harness) at the bottom of the right hand draft arm on the right side of the bowl, at the pivot point, more gears would be affected. I need more info. What does you oil look and smell like in that transmission?