Alternator?
 

I had to get a jump yesterday, was driving back and my gauges just fell, radio stopped working till the truck started running real bad, I pulled over and stopped, it was only a couple of miles. So, I came back with another battery, thinking it was the Alt, and I would just drive it home to work on. Picked up an ALT on the way. Got home, decided to check the voltage, it was at 14.5, so I turned every thing on, 13.7, checked the old battery, 11.8, put it back in and it was at 13.2. So now I am wondering if it is the ALT? could it be something else?

2003 f150 4.2l

not very good with new trucks is the alt. one wire ? if has more than one check voltage regulator