ghost in the machine

a while back my truck started acting crazy, its a 1992 f-150 straight 6 efi with 5 spd trans, well it starts and you have to rev it for a while in order for it to stay on, if you don't it will cut off especially if you put it in gear and try to go.....well i got a new car two weeks ago and ive been driving it, this morning i got into the truck and drove it to work and the damned thing never got to anywhere in the normal operating temp zone....its stayed in the cold zone the whole 35 miles, i figured it had to do with me having the heater blowing on full the whole way here, but when i went to lunch i drove it for about 45 minutes, with the heat off and it barely got to the lowest "normal" reading on the gauge, could it be as simple as the thermostat sticking open?

Yes

i got home yesterday and opened up the radiator, and it was bone dry along with the coolant jug, filled it up, drove around and still the same problem

The 4.9L is a pain in the butt to get it full of coolant. The easiest way I have found is to push down the upper raidator hose and block it in the lowered position and remove the radiator cap and let it run, filling it as it heats up. Then with a buddy's help, rev the engine up to around 1700 RPM, fill the raidator to the top and cap it. Let the engine run for about five minutes then shut it off and let it cool. After the cool down, fill the return jug to about 1 inch above the hot line and then restart and let it run. It should suck the level down below the cool line and you will see the jug fill, hopefully just short of the hot line. If it doesn't, you still have air in the system. This also applies to the 5.0L that sends coolant through the intake. The Intake is higher than the radiator. They are a rear pain to get full.

thanks i filled it already but im still not getting any temperature reading, im gonna try the temp sensor first and then we'll see what happens