I tried LR Scott's suggestion and disconnected the MAF with no change.

I then came across a post on an Australian forum about a guy who had similar problems. He said he cleaned the stepper motor (idle air control valve or IAC) and the problem went away.

I'd also read that the plenum can get pretty dirty which causes running issues.

So I pulled the plenum and as I pulled it off, I noticed that one of the velocity stacks in the ram air area was knocked over. I could have hit it while jiggling the plenum cover, or it could have come loose while driving, or some previous unknown mechanic could have knocked it while replacing the plenum - impossible to know.

Long story short: I cleaned the plenum, ram air, stepper motor and tps, and re-assembled. It's now been about 3 weeks and the truck has not stalled once. Right before I did all it was getting to the point where I could rarely take a drive of any distance without hesitating or stalling, so I'm cautiously optimistic. Not sure if it was the velocity stack or a dirty stepper or plenum or what, but something made a change. As the whole process only took an hour or so, I'd say do it all.

Thanks to everyone who suggested fixes and I hope that this is a closed issue and this post helps anyone else in the future suffering from 'The RRC Mystery Stalling Issue'