Running down why my 4 wheel drive wouldn't engage.
Raised the truck so the tires were off the ground to see which driveshafts were turning in 4 wheel drive and in 2 wheel drive. Found that the actuator at the transfer case was working properly. Tracked it down to the front actuator. Removed and bench tested the actuator. Found it wasn't working. Bought a new one and installed it.

Update: About a month after this video I discovered that I also had a bad plug that plugged into the actuator. It wasn't making a good connection. Which was why I was having trouble getting it to engage. Went to a salvage yard and got another one. Problem solved.