If you replace the lift pump and the overflow valve was the problem you will have wasted your time and money. I'd try temporarily clamping off the return hose from the injection pump while watching the fuel pressure as described by others. If the pressure is low with the hose NOT clamped and then jumps way up into the acceptable range when you clamp it, the overflow valve is the problem. If not, it's either the lift pump or a restriction somewhere before the lift pump.

You definitely have a fuel issue. Allot of good info on this thread. If none of those work. look for fuel flow problems, starting with the tank. I had a sending unit issue just like that.

make sure to check for shorts

I had to replace my mechanical pump about 2 years ago (...but mine was leaking diesel). I don't really remember how much I paid, but I'm fairly sure it was less than 100 bucks and it was from this online site. It's listed for $122, currently ...free shipping, though.

Airtex Fuel Pump Direct OE replacement

This forum has a section for finding parts, you can try there for better prices.
Price Quote - Request A Price - Diesel Bombers

i noticed the other night while lettin my truck idle that the voltage meter in dash would drop in and out without changin the rpms and the guy thats breaking our horse told me he had similar issue and he replaced his trans and it still did it then he found out it was his pcm anyone else think thats the issue

Yes, I have an idea. That's your grid heater. It's absolutely normal. Read your owner's manual and it will explain all of this. Every year, at about this time, it starts getting cold. That's when the posts start about the "weird voltage fluctuations".

If you know someone who actually replaced their TRANSMISSION over this, you may well know the person who wasted the most money ever because of the grid heater. This is somewhat like someone hearing the "snap snap" sound the sparker makes in a gas stove, panicking, and having the sewer pipe in their neighbor's front yard replaced. Completely unrelated AND expensive.

well he didnt change his trans due to the voltage drop he had the other issue im having with my truck boggin down and dying but i found out later his truck wasnt diesel so that dont help me anyway but thanks for the info about the grid heater

My dads truck done that the hose was busted off of the afc

i new to diesels can you let me know what the afc is