Many posts in the Cat engine section of the Power Train Garage, on poor performance of the Cat, ( C-7 330 HP ) HUIE injector pump , failure warning signs. Rough idle and increased cranking to start are two of the main problems, but there are other parts of the fuel system that need to operating correctly for a smooth running, easy starting, engine.
There is a back pressure valve at the transmission end of the cylinder head, that needs to be operating correctly, for proper performance.
I'll have a glace at what's there and give you the name of the best posts for info.
On the second page in the Cat Engines section, look for
Technical Article on HEUI Systems
a couple of very good links to articles on the fuel system.