After we spent hours on the phone talking with Haldex, Cummins tech support, compressor rebuilders, and a local diesel mechanic ( who was familiar with our older Cummins) we finally got an answer. Our local elderly mechanic stated after everything we did there was no way it should be dropping 25 psi in an 8 second purge. So, we ordered the lower housing repair kit for the Purest Air drier (P/N DQ6053 for $55.95). We purchased it from Anything Truck.com - their tech said he thought it was the purge valve also. We took it all apart and it looked clean- nothing to indicate it was worn out. We put the new parts in - new O-rings, started it up and the compressor went to 125, purged and only dropped 5 psi at each purge like it’s supposed to - allowing the governor and unloader to work correctly. Compressor finally turned off like it’s supposed to - problem solved!
Compressor Rebuliders - 708-430-0030 talk to Bill or JR. The compressor (QE 296C) was only $315.00 with a $200.00 core - included in this is shipping both ways. Cummins wanted $1400.00 for a remanned one, plus shipping!
Anything Truck was amazing to work with!
Hopefully, this will help someone else!
Thank you all for your help!