[Richard]

Bob,

I don't have a Trueline system, but I did stay in a Holiday Inn once.

Seriously, I read the manual cause I was interested. Neat system. Do you have the manual? If not it is here. https://www.google.com/url?sa=t&rct=j&q=...2982,d.amc

Since the system levels correctly in leveling mode, that does seem to rule out an error with one of the sensors or the computer brain. I suspect because I had this happen once, that the travel solenoid valve for the left rear may be stuck closed.

Toward the end of the manual is a section on how to force the solenoid valves open one at a time. I suggest that you force all four of the travel solenoids (one for each corner) open and observe the behavior of the coach. That will at least close in on the problem.

When the offending travel valve is identified. Force that valve open. Take a steel washer or screwdriver and see if the solenoid is magnetized. If not, check the voltage going to the solenoid, and ohm the windings of the solenoid coil. If it is magnetized you will have to disassemble the solenoid valve to unstick it, although I might try a light tap with a persuasion tool first.

Hope this helps.