One of the things I learned about a ZF6 is that the tranny temp can go way up for a long driving for towing, etc. The temp goes up in the bell housing and impacts the hydraulic system that controls the slave cylinder. It also causing problems on the clutch also and is the reason that the DMF never works well. I had a friend who did some long towing with a South Bend Clutch and it got damaged. I had a tranny cooler on my truck for ~ 5 years and have had no problems. Seems that anybody doing more that easy street driving should get a transmission oil cooler kit into their truck. I can probably help anybody with this: