Hate dredging up an old post, but it sounds like I have the same issue. Just got back from the Baja 1000 and had a couple of issues, specifically with 4x4 Low.
We had winched out several race cars from a silt bed the first night of the race and I had been in 4x4 Low. I left it in low overnight and the next morning after we packed up camp I went to swap to 2wd and it totally disconnected the drive and I was essentially in neutral regardless of what I tried. The computer gave me a message on the dash to check 4x4, the same message my buddy got in his raptor a few weeks prior when his passenger side wiring harness was melted by the manifold! Eventually I got it to shift to 4x4 high and subsequently into 2wd, but not without a momentary grinding noise followed by a loud clunk. For what it's worth, it was fairly cold that morning.
I attempted to avoid using 2wd the rest of the trip, but while driving the race course backwards from mile 80 toward 800ish (this was day two, so no race cars were on that section), I eventually came to sections that required 4x4 high. For the rest of the afternoon I was able to swap in and out of 4x4 high with no issues.
Later that night we went to rescue multiple other race cars and in the process of pulling 1064's broken chase truck up a steep silt hill I needed 4x4 low. It wouldn't shift on the spot and wanted me to pull forward...an awkward position to do this in when you're on the side of a hill with moon dust everywhere trying to pull a monster-sized chase truck up a hill. Rolled her back a little bit and drove forward, got it into low only after a grinding sound and loud clunk. No further issues shifting between high, low, and 2wd.
Bad solenoid? Something worse? Fairly disappointed with this problem to the point of complaining to Team Toyota when we winched them out about the lack of a Raptor-like Tundra (I sold my Tundra and Land Cruiser to get a Raptor). Apparently Toyota USA cannot convince Toyota Japan to do it, but that's neither here nor there.
Previous owner bought some type of aftermarket warranty ("Mechanical Protection Plan" ?), I have no experience with this type of warranty but fingers crossed the dealer will accept it.
Thoughts, Ideas? Seems to me that starter solenoids that are going bad usually have more issues when it's cold out, could that be my clue? Thanks guys.