The other day while I was driving I noticed the truck sometimes would pull to the right, after awhile started to smell something and pulled over and a cloud of smoke came off the brake caliper, I just put new pads on and it nearly ate them up, what caused it to lock up like this while driving?

 

The brake caliper is bad or the rubber brake line is bad.the caliper holding pressure on it. And its not releasing when u release the brake pedal.

 

Heat. I've been in that position before.
Good thing you caught it early it has a potential for fire and damaging other parts. Your calipers likely seized. Should replace both sides, may as well do the rubber hoses as well. Check hub carefully rotors usually warp under that heat stress

 

You just did your brakes ? Caliper or sliders could be sticking. Sometimes the hoses do collapse internally, you can force fluid in with the pedal but it doesn't flow back easily to release them.
First thing I'd check though is if the caliper pistons move easily, and if the sliders are ok. You don't say what year your truck is so I don't if you have slider pins or the rubber center inserts, but either way they have to be nice and shiny and properly greased.

 

I have had several calipers stick after changing pads. It happens.