Sounds like a lift pump problem to me.

 

Oh wow 83 chevy 4x4 with the 6.2l reminds me of when I was a little kid in dads old scottsdale it did nothing but haul firewood 160 some odd days a year for years as well as orchard tree props the rest of the time with two other chevy's next to it. Till it started to produce way to much blowby n dad put in a 350.

Tell your mechanic he's stupid that's a detroit diesel not a cat motor. I agree with airbornf sounds like a lift pump but crack injector lines n crank it over to see if it's getting fuel to the injectors.

Back to the cummins forum I got good luck hope you get her figured out.