The VP44 pump is the major issue in those trucks. If the previous owner has not been diligent in changing the fuel filter regularly, the pump could have been run with low inlet pressure, scoring the rotor. Many pumps died early on because the supply pump was unreliable and would not provide enough pressure to keep the VP44 properly cooled and lubricated. Those trucks need to have a fuel supply pressure gauge or warning light installed. If supply pressure runs below 5 psi on a long-term basis, the pump is toast. One of the first upgrades I did to my truck was to put a Vulcan pump relocation kit on and switched to a Holley Blue fuel pump. This puts the pump on the frame rail just in front of the fuel tank so it doesn't have to pull the fuel all the way from the pump to the engine. If the VP44 has been run with low fuel pressure continuously, any pump with more than 80,000 miles on it is living on borrowed time.
I did the supply pump ugrade at about 100,000 miles, and my VP44 lasted to 193,000 miles, at which time, the internal electronics board had a fatal failure. This is the second flaw in the VP44 pump, and it's unrelated to fuel pressure. This is basically thermal fatigue of the electronics from daily warm-up and cool-down cycles. It will last for "X" number of cycles, and that will be that.
Go to bluechipdiesel.com to read up on VP44 pump failures. I bought a rebuilt pump from him with a NEW circuit board and put it on my truck at 193,000 miles and it's worked fine so far. I have about 243,000 on it now.
The Cummins engine itself is anvil-strong, and I don't think mine really finished breaking in until it got to 200,000 miles.