If you can drive 500 miles pulling a trailer without a hiccup, then disconnect it and the problem immediately starts, I don't ignore that. I start asking, "What changed?"
Most people assume the trailer is the hard part on the transmission. But towing changes a lot more than just the load.
For example:
Tow/Haul mode may turn off when you disconnect.
Transmission temperatures begin to change.
Engine load changes dramatically.
Torque converter operation changes.
Shift strategies change.
Even the trailer wiring could be affecting an electrical issue.
I've even seen a trailer with a wiring problem mask a bad ground on the truck. Unhook the trailer, and suddenly the truck starts acting up because the electrical path has changed.
The biggest mistake would be to assume the transmission suddenly developed a problem because the trailer came off.
One thing I've learned after almost 40 years is this:
Don't focus on what happened—focus on what changed.
Something changed the instant you disconnected that trailer. My job would be to figure out exactly what changed: the load, the programming, the temperatures, the electrical system, or something else.
That's usually where the answer is hiding.