Am I right on my Troubleshooting codes PO171 & PO174?

[Nodnarb76]

I've got 12,00 miles clocked on my 6.0 LS swap from 3 years ago.
Yesterday when driving around, CEL came on. I checked for codes and got PO171 & PO174 lean condition on both banks.

When I did my swap, I installed a fuel pressure gauge on the fuel rail.
I noticed I'm getting 40 psi (according to the gauge). I'm thinking this is the cause of my problem.

Could my fuel pump be bad? I used a Walbro 255 that was brand new, would it have gone bad in 3 years/12,000 miles?

Also what are the odds either my filter/regulator is clogged or maybe the inline fuel filter under the truck is clogged.

I know to also check for vacuum leaks, but If my gauge is correct on the fuel rail I'm guessing my fuel pressure is too low.