I have the same Sub which was abandoned by the owner,who died a few years later.
He had spent a bunch of time trying to get it to run as well.Long convoluted story.
After i heard he had died his son called about it,i told him the bill owing on it prior to the death and he said keep it.
The catalytic converter was plugged solid,it would just start and die,once i undid the converter it fired up and ran great.This one had been driven till it couldn't run anymore. The soot the came out of the exhaust made a huge mess in my shop so do it outside.
90 Chev 3500 c/c 4x4,6.2na,400 auto,4:10 gears.DSG Timing gears,main girdle, isspro tach, pyro,boost,oil and trany temp.Dual Tstats, High volume peninsular pump,on shelf, Custom turbo and intercooler 85%complete. Change of plans for the dually, it's going to get a Cummins. Both trucks are Blue 90 4x4 crews