Ok need E4OD help or suggestions.

Hey guys I have a 97 F350 CC long bed w/just under 150,000mi. I just bought my first enclosed trailer. I have pulled my race car on a 18ft. all steel flatbed up until now and never had one issue. Well I went went and picked up a 30ft tag with 1ft. extra height enclosed yesterday. Well truck pulled trailer pretty well. But cpl hrs into the trip on smaller rural road where speed was limit was slower it kept switching between gears it seemed, That or TC was locking up and unlocking. it mainly did it around 60mph. But several hrs later when I was almost home it was doing this even at like 40-50. When I would get truck up to highway speed like 70mph it pulled great and had no trans issues. Any ideas what it might have been for sure. think I hurt trans? What do you guys suggest to fix this problem and keep me from having it or anymore problems. especially once I get it loaded with my car and tools and 4 wheeler or gold cart for a weekend of drag racing. Thx.

Take it out of overdrive unless you can do at least 65

Also flush the Trans and put amsoil in it and look into a tigger kit for it

Tigger? Tugger????

Oops. Tugger. Damn smart phone

I had that same style of truck you got a few years ago. I had over 4 grand in the tranny because mine was doin the same thing your is doing but I kept breaking the intermediate shaft. So with thay problem I bought the billet one an put in an fix that prob but didn't fix the shifting and all I did was drive it to an from work. I ended selling the truck well soon after I did that I found that in guess there's a sensor in with the valve body that goes bad from what I was told. Not sure if this help but thought I would enlighten you.