If it runs that good once started and is just hard to start cold, I doubt it is your injectors. In all probability, it is not the pump either, unless you have a seal allowing air to get into the system.
My bet would be your glow plugs are not getting the job done for you or you have a fuel leakdown. Take brake cleaner and spray the base of your fuel filter so it is dry, then see if you can detect any leakdown, moisture the next day.
If you can get an assistant, open the bleeder valve at the top left of the fuel block to see if you have air in the filter. Have assistant crank the engine while you open the bleeder. It is a black plastic screw with a cross on top. The fuel should flow out the vent to the left almost immediately. If it spews bubbles, you have a leakdown problem.
My M1009 had two problems, the drain valve at the bottom of the fuel block was draining slightly and the check valve in the lift pump was not holding the prime. It would run great all day, then not start after sitting 12 hours. Slow down the cranking in the cold and it was done, the batteries would die before it would light up.
It has run perfectly since swapping the lift pump. I wa not aware of the lift pump holding the prime until I visited my local pump shop. He suggested I start with a new lift pump.
If you decide to swap the lift pump, it is a tough chore on these. There is a push rod that runs inside the block and drives the pump off of a lobe on the camshaft. That rod has to be in the up position when you install the new pump. If it is down, you will bend the rod and most likely ruin the new pump. The hole it sits in is not a pleasurable place to work. In front of the engine mount, behind the lower radiator hose and battery cable. There are also two fuel lines to contend with and a cup in the corner of the cross member.
If you pull your lift pump and the rod slides down, you will be pulling the fuel pump plate as well. On my first M1008 the lift pump was leaking and I changed it out. The block plate was not glued to the block, I removed the two lower bolts, cleaned everything up and it went back together fairly easy. Not the case with this M1009. Somebody had used that black hard gasket sealer to glue the plate gasket to the block. It took about three hours with a half dozen razor blades to scrape that crap off.
Other Chevrolet V8s have a set bolt in the block that you can remove and replace with a longer bolt. That is supposed to hold the pushrod in place. I have never used it though, I had a buddy crank one down too tight on a small block and got the rod stuck in the bore. We had to tear the engine down and drive it out.
If you remove that rod, use axle grease to hold it up in the bore while you replace the pump.
Before spending 300 dollars on an injection pump, I would try the 20ish dollar lift pump first.
Before doing anything with the pumps, I would try removing the air cleaner and misting some diesel into the intake with somebody cranking to rule out the glow plugs. It should fire and run off of the misted fuel, at least for a few seconds.
In my limited 6.2 experience... these engines go down to rod and crank damage long before they go down on compression, providing they have good air filters and have been serviced regularly. Glen
