I have a 97 E350/V10 under a 24' class C motorhome. It has 102K miles and I am assuming it has an E4OD. About half the time I use the vehicle I tow a 3,200lb Jeep. On my last trip I pulled the Jeep and did not notice any problems with the transmission on the way to the camp site which was about 120 miles away and no significant grade. On the way back, in the last 50 miles, I detected something wrong while cruising between 60-65mph in OD. It seemed like the transmission was either slipping or hunting for a lower gear. In retrospect, I realized it was barely detectable because my wife did not feel a thing. The only evidence I could come up with was that my RPM, as read from my Scangauge, was jumping from around 2,000 to 2,300 for barely a second or two. Almost undetectable for the Scangauge. The cruise control also stopped working during this time.

Thinking the transmission was kicking out of OD, I hit the OD button just to see how much of an RPM change I got which was around 900 RPM, no where near the 300 RPM I was seeing. I pulled over to check the fluild level and found it to be fine with no discoloration or odd smell. I keep driving until I saw the temp rise to 185 (which seemed high to me at the time) at which time I pulled over and disconnected the Jeep which my wife drove home. I did not have any issues the rest of the way home, even the cruise control worked again. Since I have the Scangauge, I checked for codes during the event and none were found (no flashing OD light either).

One other piece of info, about 9 months before this trip I drove up a very steep road to campground without pulling the Jeep and before I figured out how to program the Scangauge for trans temp. When I got to the campground, I back up a ramp to level out the RV and dump about a quart of fluid from the front of the trans. There were no detectable leaks or problems after that.

Any ideas as to what's going on with the apparent slipping that I detected? I have read through many posts on this, and other, sites and could not find this same issue. Most seem much more severe.

 

The small rise in RPM is the torque converter unlocking. If there is something wrong in the brake light circuit this will happen. It will also disconnect the cruise control.

The first thing to check is the wiring for the towed vehicle. It seems to work when that's not connected.

 

That certainly makes sense. I will check that out this weekend. Thanks so much for the help.