GM's approach to a cleaner diesel took an approach which makes it behave oddly, and in each year since the ECM controlled fuel injection pump was introduced, a slight change makes that engine behave differently than others in the 6.2 / 6.5 family
Here is the secret issue - the lift pump is undersized - likely due to trying to make emissions lower. Use of a 1992 to 1993 (part number E158 or EP158) lift pump rated at 8 to 14 psi will solve most all of its problems
Often you see questions like Lucas Oil Stabilizer vs Opti-Lube Oil Fortifier?
Then usually "know nothing" people all weigh in and all usually support their own shortcoming sayng "there is already an additive in the oil"
There was a diesel "heavy duty service" CD-4 type oil for a reason - the Diesel engine beats on itself, but those oils do not mean the manufacturers put the very finest of everything into the oil they sell. 15w-40 and straight 40 are common diesel oil products.
The Stanadyne DS4 injection pump is the electronically operated version of the DB2 mechanical pump on early 6.2 Liter GM diesels. It can be finicky if you mix and match different DS4 units with different EPROMS not for the ECM that controls it. It can be hard to troubleshoot also.
There are a lot of articles all over the web where well meaning people are trying to explain something they truly do not understand. The Chemistry of PETROLEUM and its refining.