Hi - this is a problem with the transmission going into limp mode. This happens when the transmission control unit detects certain faults & to diagnose correctly will need a diagnostic tool that can read the faults stored in the transmission ECU. In the first instance however I would recommend checking the electrical connector on the side of the transmission to see if this has been disturbed during the recent work carried out - try disconnecting & cleaning the connector with electrical cleaner, also checking for any signs of transmission fluid inside the connector.
If transmission fluid is leaking into the connector then the plastic spacer insert with seals should be replaced that is located in the tranmission casing that the connector plugs into.
After this a check for fault codes will be required to pinpoint the fault.
Problems with the speed sensors on the electrical plate inside the transmission are common on this model.
A check for leaks & rechecking the transmission oil level would also be a good idea at this stage
Best regards, Paul
Hi, Are the speed sensors easy to replace if the problem lies in these sensors and are they expensive? Shaun