The other day I started the truck and the ABS and Airbag light came on, and when I was moving the speedometer didn't work either. This incident so far is a one- timer. and hasn't happened since then. What would cause this?

 

Failing vehicle speed sensor. I am going to guess that you have a 98 or newer 2nd gen? If so, the sensor on top of the rear axle is the culprit. That's where PCM gets its cue for vehicle speed.

 

UPDATE: I later realized that when that happens my Air conditioning does not work. The second the AC kicks back on the speed works, and lights go out. As of now I don't know of any further issues. When My dad was borrowing the truck he claims that, the ABS, Airbag, Speedometer, and the AC did not work, and then kicked back on again.

 

Ok, that's going to be a different issue. If you don't have one already, download the service manual for your truck from here. See where those system get power from, there's got to be some commonality there. (and it might be as simple as the ignition switch.)

 

I had the same thing happen,but when I turned on the ac everything worked fine.
I think it is a computer glitch, should have never put computers in trucks