Hello Brian and Welcome - My name is ***** ***** Im happy to help / advise you .. I am sorry to see you have had a wait.With the issue of left foot braking - whatever reason you do that, that is feasible that as the dealer says, that could "confuse" the Ecu / Pcm - master computer... as it relies on correct signals from the pressing of the accelerator and brake pedals ( from there switches ) to tell the Pcm exactly whats happening -and that then commands the gearbox accordingly - So yes - that certainly could be the answer there..Obviously you need to try and drive w/out doing that for a good while and see if the situation "cures" .... If it does, you know thats the cause of the problem you outline.Other than that - the gearbox on your XF is fully electronically controlled - commanded by the gearbox Tcm ( computer ) which again as above, relies on the inputs of the various switches / sensors as to how it commands the transmission to operate. As such, this system is fully diagnosable by computer- It will need if you still have the trouble after driving as above to be connected to a suitable ( Jaguar ) diagnostic machine. This will first interrogate the Tcm for any logged fault codes which can then be sorted out and then see how it is. If there are no fault codes, the car can then be driven while the machine runs Live Data checks to find the fault that way.So one way or the other , working through as above is the way to get to the bottom of your issues there.If there is anything more you need or would like to discuss - by all means get back to me and we can carry on....>> Meantime ...........Please do click on the "OK/ Excellent ratings" for me as that's how Im credited for helping you - Thank you in advance for that...You can and are most welcome to get back to me anytime you might need - clicking the OK ratings does not close you out at all..Kind Rgds Brian - MIKE.