2010 Cummins isx burning coolant

I’ve got a 2010 t800 with a Cummins isx. Bought the truck a few months ago but it’s been sitting. Finally getting around to getting it roadworthy. Took it out for a short ride about 20 min. While driving it was puffing white smoke, and the coolant level alarm came on. When I got back the coolant reservoir was empty, so I added 2.5 gallons or so. Took it for a ride again and same thing. Coolant is getting into the exhaust and being burnt. from some quick research it can be many things; head gasket dropped liner, egr cooler.
Service records show the truck has had coolant loss issues in the past, it’s been pressure tested, no loss, ruled out internal/external leak. Radiator has been replaced.
I am thinking it’s possibly EGR cooler? I would like to start trying to diagnose so I can figure out if it is the cooler I can send it to the mechanic to replace it, but know it won’t be cheap.
any suggestions?

 

The oil level hasn’t changed and it doesn’t look like it’s going in the oil. It doesn’t appear to be leaking out of the reservoir from pressure build up. It’s most certainly coming out the exhaust, but it’s not constant. I talked to a few people that said head gasket, but based on the pressure test I don’t believe that it is, but I would have to pressure test it myself to verify.

 

I’m trying to diagnose to see if it’s even worth putting money into or not… I have a feeling it’s needed a rebuild but don’t know if it’s worth putting 30k into.