Bad injection pump?
 

I'm trying to help out a buddy who has an 01 that has had an extreme loss of power and mileage has tanked. The truck is a auto and the only mod is a turbo back exhaust. It also has under 100k. He had the truck in to the dealer and was told the outlet presure on the pump was bad. He's ready to throw a new pump on it but I hate for him to that without knowing for sure that the pump is the problem. I'm trying to get a scanner so we can see what codes there might be. Any advice would be greatly appreciated?

First thing I would do is get a fuel pressure gauge and check the psi on the old pump should not drop below 10 psi. Your not wasting any money on buy the fuel gauge to check the pump cause if the pump is bad your gonna want to put the gauge on the new VP44:tu: To check the codes just turn the key to on then back to off a couple times stopping in the on position. The codes will read out in the mileage screen. Dont start the truck during the keying.

Are they saying the pressure is bad on his Lift Pump or Injection Pump?

They are saying presure is bad at the injection pump. I believe the truck had a new lift pump within the last 6 months. Could running earlier with the bad lift pump have caused the demise of the injection pump?

Yes it can cause premature wear to your injection pump running with a weak lift pump.

Here's some good reading on the VP44.
Blue Chip Diesel Performance Specialists

You need to find out what the LP fuel pressure is.