There are several switches attached to the Tip, one is at the shift selector lever and tells the control module which position the selector is in. I suspect this is where your problem is. The housing, around the lever, has to be removed to access and test it. If it isn't that one there is another on the driver's side of the trans. The only other one, I could find, is the actual pin position in the control module wiring harness that is also listed as a switch to trans ECU.
Personally I'd start at the shift lever switch as it sounds to me like it is not engaging the rest of the switches to tell the ECU it is in M.
Hope this helps.
