Thought it sounded like a wiring issue. There would have to be 2 bare wires contacting the box or 1 wire with the box itself grounded to the engine to cause an issue. Or a break in the copper strands of a wire. If it is an old style unit with rubber grommets you may be able to unscrew the cover and take a peek at the wires inside.

Be careful that you have adequate slack in the wiring if zip tied to a heater hose. Did that once and when I fired up the engine it yanked some of the wires out of the throttle connector.

 

Looks like I'm having a similar issue. I get code p2135 under WOT. I'm using an ls3 TB (gold blade) with I'm assuming a newer version xlink as it was bought this year. Running the stock truck throttle body no error codes. I've seen other people have the same issue and switch to an ls2 TB and it sometimes clears the issue. I'm assuming those were earlier versions. Thoughts? How do I verify the version of xlink I have?