Ok, so after finding the part # for the return line check valve myself since my Deere dealer couldn't find it and thought it didn't have one, I have replaced the said check valve that my unit supposedly didn't have.
While I had it out, I put in a regular barbed fitting, connected another chunk of fuel line to it going to a clear container, and operated the hand prime until I had pumped out about a quart of fuel, per tool-king (Ed) recomendation. It did appear there maybe could have been some junk in the fuel rail that could have been getting stuck in the old check valve. Put it back together a d hand primed about 5 or 6 pumps and it firmed up solid, unit fired right up.
I started it before working on it so I could raise the boom up to raise the cab, and prior to starting I pumped the hand primer about 20 times and it never got firm, which leads me to believe the check valve was hanging open at least partially, and it ran like crap as usual at startup.
I'll fire it up again Friday after it sets for 2 days and will report back again. For anyone that doesn't know tool-king (Ed), he is a first class guy and more than willing to share his knowledge to help a guy out. I am pretty mechanically inclined, but outside of regular maintenance on my Cummins (oil changes, fuel filters, etc), I have very little experience with diesel engines. I spoke with Ed several times today via phone calls and texts, great guy and greatly appreciated.
I'll let you all know how it goes Friday, hopefully this finally puts my startup woes to bed.