Ford 7.3L Power Stroke (1999-2003) :: 4R100 Trans Won't Go Into 4th / OD Light Flashing And Occasionally Overheats

I have an early 1999 Ford F350 4x4 7.3. I purchased it used about a year ago. The trans was replaced with an ATS 4R100 and a billet torque converter. I have the paperwork for it to confirm it along with the mileage when it was installed. It currently has about 35k on the new trans.

Several months ago the trans heated up to about 200 degrees on my trans temp gauge that was already installed when I purchased it. Not a huge deal and after pulled over and high idling it off I went and no problems.

About a month ago I was towing my fifth wheel when I noticed the temp rising on a level grade. I also noticed the OD light flashing. I made it home and when I went to drive it the next day light was not flashing and it shifted and drove like normal without the trailer.

I towed the trailer again and same thing, OD light flashing and started heating up. I changed all the fluid and flushed it based on the trans flush procedure I got in this forum and replaced with an OEM trans filter. Towed the next day and everything was good. Temp was good and no OD light flashing but I lost 4th gear. All other gears shifted fine, no slipping, just won't go into 4th.

On my way back home the OD light started flashing again and instantly the heat started rising on the trans again. I was finally able to get it into 4th if I let off a little, but as soon as the OD light started flashing I lost it again.

I have a friend of a friend who works for Ford who offered to come over to hook his scanner up. When he hooked it up there was no stored codes from the OD light which we both thought was odd. Took it for a test drive and the OD light started flashing so we could get some readings. He said it showed an error shifting from 1 to 2 and another error when shifting from 3 to 4. I unfortunately forgot to ask him for the specific codes. He tried to read the torque converter info but said my truck was to old and the PID was not supported to read that info.

He said it appeared it was mechanical but without some type of break out box where he can physically shift the gears he couldn't say for sure if it was mechanical or electrical. He did not seem to interested in doing that test for me as he rebuilds trans on the side and said he could rebuild it for me.

It seems my overheating takes place when the OD light starts flashing. It still drives fine and shifts smooth with no issues with or without the OD light flashing. 4th gear usually doesn't work but on a rare occasion it will go into 4th fine which makes me believe it may be electrical.

I am new to diesels but have learned a lot about my 7.3 lately. I recently installed injectors, up pipes, hutch mod, and several other little things so I can get things done myself but am just a DIY'er who can follow good directions. I know very little to nothing about transmissions though.

While working on another issue I did notice there is a large wiring harness that connects up on the driver side of the trans. I unplugged it and was checking the wires and after removing the dirt and crud on it you could see the outside wire sheathing had deteriorated exposing the copper. I bought some liquid electrical tape and sealed everything up. I did look for a replacement wire harness at the time and the one I ordered was very similar but the plug was different so that is why I used the liquid tape at the time. I did not seem to have a problem at the time after fixing it but wanted to mention it here in case that may be an issue.

I also thought swapping out the solenoid pack may fix it. I did not want to drop the trans and send it for a rebuild if I did not need to. I know there are some other sensors associated with the trans like the TSS I think but don't know if they are even related to my issue.

I tried getting the codes from the guy but he does not have them and I can't get him back out. I have an OBDlink device connected to Torque on my phone but I couldn't get it to read trans codes. Could be user error.