Truck's been sitting for several months & was finally able to get out yesterday outside temp was about 32* & after an hour on the freeway @ 70 mph gauge was still @ the 140* mark & little heat from the HVAC. I'm thinking it is the thermostat since on a good pull it would gain a bit of heat but not much. Any other ideas ?

 

My Dad's 97' was the same way the thermostat is more than likely stuck open, either from rust, or something has broken causing it to say open.

 

I would start with replacing the T-stat. While youre at it, give it a good coolant flush and replace with some quality stuff. If that doesn't help, block off part of the radiator with cardboard or the like. That should build up a bit of heat.