Ok, heres the problem, the truck overheats, we find out its leaking coolant and now theres none so we fix the leak, next we find out there is now no heat, so we change the thermostat, still no heat. Is there something else that could be done for a DIY'er?

 

You probably have to bleed the air out of the system.

 

It's been done. I'm not the truck expert, my dad is, is there anything else that could be causing the problem?

 

Doesn't the 4.2 have issues with head gaskets? I thought it did. I would say you're sucking air in through that gasket leak and not getting proper cooling.

 

The air is automatically bled from the lines, there is no oil in the coolant, the coolant light is on, so maybe theres just not enough coolant. There is a little bit of warm air coming through, just enough so its not freezing inside. Any other theories?

 

It might be helpful if we knew where the leak was,and how it was fixed.
Ive heard of bad intake gaskets on the 4.2,as well as head gasket issues.I personally have had no problems with my 97 LWB with the 4.2....I DID however have to replace the Air Blend door module...The truck came from a relative in Louisianna,and they dont usually need heat,I bring it up to Memphis,and the first cold snap....nothing.
Im not saying this is your problem,but there is the possibility that you actually have two issues.....

 

The bad intake gaskets were corrected by 99.I didnt think of the blend door. You might want to check that as well.