Check gauges problem?

I have a 2005 or 2004 Ford sports trac truck. A couple of days ago the check gauges signal came on. I looked under the hood and saw that there was no water, so I filled it up. Still the check gauges signal comes on. Today I was sitting in the truck while it was parked and had the ac running. I turned off the ac and the car about 30min Later. Then when I started the car again it sounded like it wanted to turn off and it kept shaking. I had to press the gas pedal just so it wouldn't turn off. Anyone know what the problem could be?

Do an OBD2 code check. Guessing is silly when you can get a real answer from the car's own computer.