X5 3.0d sport transmission problems

[Wicksyp]

Hi, first post so here goes!!!

My wife's x5 e53 3.0d sport 2004 facelift is experiencing some transmission issues and I have no idea wht to do next - would appreciate any suggestions!

The symptoms are:
Car drives perfectly when cold, however when it warms up, the displays 'transmission fail safe mode' on the dash, the PRND symbols all illuminate, along with the abs light, the 4x4, the brake fluid light and the airbag light. Switching the car to sport or manual has no effect and occasionally it goes into limp mode.

The car has been checked for fault codes and comes up with - can bus communication error.

So far the following work has been conducted:
New transmission fluid
New genuine zf mechatronic valvebody
The valvebody/gearbox has been reprogrammed to current BMW specs.
An auto electrician has tested the can bus points individually from the gearbox to the transmission control module and abs pump and they are all transmitting correct readings

The issue appears to be intermittent. if I stop the car, switch off and switch on, it restarts and drives for a few miles then all happens again.

Then the strange stuff.... I drove the car 25 miles this morning without missing a beat. The only difference was that the mechanic had left the undertray off the bottom of the car....

This is telling me the fault could be temp related.....

Any ideas please?