Intermittent - 6L80 Issue: Current Gear vs Gear Selector Position

Hoping someone may have some insight or potential diagnostic procedure on a strange issue I am having.

I have a 2007 L92/6L80 swap into a Land Cruiser. 9 out of 10 times, I can start it up and throw it in drive without issue. Sometimes, however, when I stick it in drive, the truck feels like it is stuck in 3rd or 4th gear from the get go. If I turn the truck off, let it sit a second, and fire it back up, the problem usually goes away and the truck goes back to normal.

I hooked up the scanner when it was having one of its fits, and I noticed that while the position read D6 (normal), the actual gear still said Neutral. Even with the actual gear selected being neutral, it still drives around (but feels like it is stuck in 3rd/4th). After turning it off and on again, I verified that it correctly selects 1 when the position is in D6.

No DTCs are present. Any insight on where to go from here?

Update, I found this thread that resolved my issue. It seems the URL is not working, but the thread is on the EFILive forum titled Solution for p2534 limp mode transmission on engine swaps


It had to do with the PCM staying on slightly longer than the TCM after the key is switched off. Instead of having the switched power wire for the 6L80 running straight to a keyed power source, it needs to have power given through a relay that is switched on from a ground signal from pin 59 of the E38 PCM. That way, when the key is switched off after driving, the PCM will continue to keep that relay grounded until the PCM itself shuts down completely (usually about 1 second after the key is switched off).

Hope this helps someone else in the future!