You don't have vacuum hubs, you have a live axle up front.

 

Then what would it be?

 

Sounds like its not engaging right. I would check the t-case fluid.

 

You don't even have a locker if your truck is stock. It's a limited slip.
The problem is the brakes. Ranger's with rear drum brakes locking up is VERY common. They get water/mud/anything in there and they will lock up, even on dry pavement. I have had to use 4x4 low on my 98 ranger to get them to release before.
It could be a parking brake issue but could very well be the drums too.
Something tells me that you switched into 4x4 with the rear tires spinning at some point too... Or you are getting on the throttle hard before the truck is in 4x4.

 

change your t-case fluid. Before I changed the fluid in the T-case it would shift sorta rough into 4x4 high or lo. after i changed it, it shifts nice and smooth. very easy to change to

 

While it was at ford today ( wow that was an experience f*ing stupid mechanics) I got them to cheack the level and they added a fair bit to my T case, It was a bit low.

But the main reason I brought it there was to get them to adjust my headlights, They mechanic comes out and tells me he cant he doesnt have the tools. ITS A 4MM SOCKET! and you'r telling me ford doesnt have one??

So I go in the back and show the moron how to pull the headlight out, he had no idea, and that he had to adjust all the little things not just the top one.

He also had the off road lights on and was playing with the headlights wondering why the off road lights werent moving.

I ended up taking it home and doing it myself, and had to pay $11 labour to teach a moron how to pull out a ford headlight