Did you reset the RF Hub? I know that was one of the things you had to do wit the Autel device (or what ever it is called) I know a couple others have dabbled with changing the tire size but don't recall them getting errors, it just did stick (they did not rest the RF hub)
Just came back from friends whom I borrowed my ALFAobd and laptop
So he changed the tire size using "Program Tire Size" setting in Body Computer only (not sure why as this was NOT on the list of safe changes that I gave him)
I looked at his door tag for tire size (LT275/70R18E) factory size and asked what he changed to (LT265/70R18 A/T or LT285/60R20E A/T)
He changed the tire size to be closer to his new tire (275/65R20E)
I then went back to "Program Tire Size" and the closest match that I could find to his factory programmed tire size was (BS/FS LT275/70R18E A/S).
I figured that i would give it a shot to see what happens.
The ABS error and Trailer Brake error are now gone but the accelerator pedal error remains.
My conclusion would be that the BCM and RFH tire size values must match...
The Options in the ALFAobd for tire size do not match exactly to "LT275/70R18E" which must be the reason for the error.
Since I am NOT able to enter my own raw values "LT275/70R18E" into the option list for tire size, I am unable to help him out unless I try with the A E tool, but that is untested waters also.
As an OPTION, if I can find someone local with a tool capable of updating the tire size in RFH, it may fix the error...