FYI...torque converter wont allow tranny to shift because of an over torque situation. Common with tuners.
FYI the torque converter has no control over the trans. When the PCM tells the trans to shift, the torque converter can't prevent the shift.
Limp home mode is when the PCM detects a severe transmission problem. The PCM limits the transmission operation to try and prevent damage. A lot of people say that limp home is only a certain gear, but that isn't correct. The PCM decides what the trans can still do with the failure that it has, and uses what is still useable.
An example of limp home would be if the PCM detected that the pressure control solenoid that operates the overdrive clutch didn't work. In that case 2nd and 5th gears wouldn't work, so the trans will shift 1-3-4, since that's all that it can do.
I've never heard of a Torque shift going into or having a limp mode. The Allison trany (witnessed a 2002 DMax in limp mode) has a limp mode and it will go into limp mode with a tuner and a moderate to heavy load. It is controlled by the TCM and not the torque converter... Then again I could be wrong. I'm sure some one will correct me if I am.
My 05 F-250 went into limp mode while driving once. While in limp mode it ran like it was governed at 50mph. The service department at the dealership said it was because the EGR valve was stuck. They replaced the EGR under warranty and I haven't had any more problems.
Earlier Ford trucks had it too...thr tranny was the topic of this post...my '92 F250 would go into "limp home" mode when the vss module went out and also when the fluid level got too low. It would upshift really HARD and the overdrive lamp would blink to tell you it was in "limp home" mode. Codes would also show up when I took it in for repair....Can't really remember what they did...maybe changed fluid. Finally had to have the tranny overhauled - at about 150,000 miles. Never had the problem again.