I have also had this same issue on my 05 4.8is. Driving uphill at about 70kmph and switched to TFS mode, thishappened to me twice. Luckily I always carry my foxwell in the car and I managed to clear (most) codes on the roadside and carry on my way.

I have since changed my transfer case actuator (I already knew this was faulty from testing) it could be totally unrelated but it hasn't happened since (the TFS error that is)

I still have the EGS line disturbed error though and I know I do have issues with my EGS module - Sometimes this just returns no comms from the foxwell scanner and INPA. I also have an issue with my TRS which intermittently wont allow the car to start in park but switching through the gears and resting back in N fixes this.

I believe on our models both the EGS and TRS sit inside of the transmission so you will need to drop the transmission and open it up to replace/investigate either of these I have read in a few places that the EGS modules can be a bit iffy so that's what I'm going to blame.