As far as I know there is no return line. It has the regulator on the fuel bowl but no return. That's why alot of people but regulated return kits for them

Well anyways I'm replacing it, everyone is clueless when it c9mes to this pickups issue.

Just about don't with this pickup.

Did you find the two screens that are inside the tank above the pickup tube in that plastic housing you going to open it up and are two screens in there if you didn't get those cleaned you still going to have a problem. Also how many lines did you remove from your tank they should have been the electrical line and two rubber lines because my 73 has a return line. We are trying here this is hard to diagnose when we can't be there.

Somewhat same issue
 

I unplugged the manifold pressure sensor and now I run like a rocket. That tells me every mechanically part on engine and tranny work. I plug sensor in and back to no codes no smoke no power.

Did you check the MAP sensor hose all the way to the intake Y ?
They do crack by the nipple on the Y

I had the same symptoms as you a while back on my 99. Turned out to be the rail mounted fuel pump cutting in and out randomly. Replaced it and she was all good. Something to check out at least.

Me too
 

Don't waste money on "y" pipe or fuel pump. Yet! I am currently running with map sensor unplugged. .. New parts..fuel filter fuel pump hpop rebuilt all injectors exhaust pressure sensor and tube. Icm ecm map. Turbo complete. Wicked wheel after complete turbo replaced. Gate valve is closed shut. Can't find a vacumm leak due the incredible amount of noise from the Diesel engine running in my ears. Currently sitting and flushing coolant system. Massive milkshake (oil cooler leak) last of my worry now. Back to no power. Save my email if you figure it out tell me. If I figure it out then I will be a master of diesel

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The exhaust back pressure valve is in pedestal. Plan on a new one. Buy it. Mine did the same thing for 2 years