So yesterday at 28* the truck ran fine but this morning at 18* she starts up ok but when I go to take off, she drops fuel pressure down to 5 lbs. Usually my idle pressure is 21 lbs but today it wouldn't go past 17. I just have regular fuel, not winter, and I run premix oil at one oz. per gallon which I'm sure thickens the fuel. So, is this what is happening and at what temp does regular fuel thicken up? Thanks y'all

 

Straight #2 diesel starts to gel at 20°F but if your fuel heater is functioning you're supposedly good down to 8°.
Add some anti-gel additive and you can go as low as -40°
I run anti-gel additive even though the fuel in my area is supposedly winterized.
I just don't trust the fuel companies, additive is cheap insurance.

 

Well, I just added a bottle of Power Service and ran her for about 15 miles and no difference. Does this mean my filter is clogged with ice crystals? I also drained the water valve on the filter. Just weird that she ran perfect yesterday at just under 30* and today at 23* I lost that much fuel pressure. I wonder how much having the premix oil in there is hurting me?

 

I highly doubt the oil is affecting anything but you very well could have water in your fuel that has frozen.
I'd start by changing the fuel filter and seeing what it holds.

 

I have a spare fuel filter but I need to get a new inline strainer for the FASS. I wonder if the strainer is as likely to clog?