Just brought the truck back home from the dealership, and it's running great again. Looks like the issue was premature timing belt failure, and luckily it didn't jump time far enough to cause any additional damage. The dealership performed the standard belt+water pump job, made sure everything checked out, and sent me on my way.
I have the old belt that was only 70,000 miles old when it failed. It isn't missing any teeth, but it does look pretty worn. I guess that was enough for it to fail.
Overall, I was very happy with the service provided at Cumberland Toyota in Cookeville, TN. The timing belt replacement was something that needed to be done in the not-so-distant future, so I only paid for something that I would have had to pay for anyways. I really lucked out this time; it could have been a whole lot worse. The moral of the story is don't limp your truck around if a whole bank of cylinders goes dead. Hope this helps any V8 owners identify this issue if their engines exhibit the same symptoms, and thanks again to all those who offered advice and suggestions.
The 4Runner lives on :cheers::dancin: