[olddog]

I agree with the above comments, but I will elaborate... make that speculate.

I suspect that the memory location that he is looking at is not actually the long term fuel trims, therefore what ever software he is using is not mapped correctly for your ECU.

It is possible that your ECU has been flashed to something other than what the box originally was and therefore he does not have the correct software to look at it. What do you know of the history of your ECU? Could it have been played with by someone else, unknown to you? If not, you can rule this out.

It is possible that this fellow is just not using the correct software for your ECU. If this is the case, you really have the wrong guy.

If my assumption is wrong and the actual LT fuel trim is changing, then I would say that your ECU has been hacked up by some tuner, or it is defective.

I'm no expert, but this would be my first thoughts.