05 9400 ISX 400 issues

So i have a couple issues with the truck i just bought, it's an 05 9400 Eagle with ISX 400ST.

First problem is it has almost no power, has a hard time pulling 14k lbs up a hill. Starts perfectly fine, no long cranks, doesn't smoke, in neutral it revs just fine, no rough running except that it 'sounds' like the cylinders are running dry. I've replaced both fuel filters, and when i had the fuel manifold filter off i ran the lift pump to see how much fuel was going through it and barely a trickle came out, i'm thinking my lift pump is bad? I hear it run and can feel it running, but i know just because it's running doesn't mean it's pumping fuel. Can i install an aftermarket lift pump and pump past the stock lift pump? Or if i do this am i going to have to take the stock lift pump off?

Second problem is voltage, all my battery cables are run correctly, same with the alternator cables that i can see, i get 14v out of the alternator and to all my accessories, but not back to the batteries? Not sure how this would happen but it does, no matter what the alternator is doing, i only see approx 12.4 volts at the battery terminals. Any idea on a good place to start checking this one? I'm almost to the point of running another dedicated cable from the alternator to the battery box.

 

Okay I'll look for boost leaks and a plugged sensor. So how does the ISX run then? I thought on all diesels, the lift pump fed the injection pump, and if the lift pump died then the injection pump usually quickly follows. I guess i need to get a pressure gauge and hook it up to the ports on the fuel manifold to make sure the mechanical pump is working.

And did that with the battery cables due to a hard start issue when i first got it. Brand new battery link wires and cables running to truck. Like i said, i'm getting good voltage everywhere on the truck except the battery box. Do you know exactly where the 2 cables coming off the alternator go? I tried tracing them but they go into the plastic wire wrap stuff and i don't want to open it up yet.

 

Also i was just looking at the side of the engine, why in the HECK does the intake piping right before the engine go from 4" piping down to like 1-1/2" piping then back up to 3"?!