Truck idles like crap/dies when fuel level is less than 1/4 tank, fuel pump?

[BlackGMC]

I have had this annoying problem for about a year now. When ever the fuel level gets below 1/4 tank the truck starts having some idle issues... It will surge and sometimes die... But it only does it when it is below a 1/4 tank... I am starting to think it is my fuel pump. Another reason i think my fuel pump may be weak, is my VE values in the 95-100kpa range are above 110%, i think i peaks at 115%... I have 31# 8.1L injectors and my IDC is about 74%....

I only have issues at idle when it is below 1/4 tank, once off idle it is the exact same.... My LTFTs stay about the same the no matter what fuel level i am at... The only other thing i can think of is there might be some emissions test that occurs below 1/4 tank... I have put a mechanical fuel pressure gauge on it before, the fuel pressure was good, except i had about 4-5 PSI drop at WOT...

My truck is a 4.8 with the following mods if it makes a difference.
TBSS intake, PRC stage 2.5 heads, FTI 214/220 .600/.597 108+2, 3600ish, EFILive, Efans, Airaid CAI, UD Pulley, AEM Lts, Magnaflow, DMH e-cutout, 4.10s, TrueTrac, Transgo HD2, Servos

I have tuned it with my LC1 wideband...

Any ideas?

[joecar]

It might have to do with the EVAP (fuel tank pressure) test, but I thought that it was run when tank was between 1/4 and 3/4, and while driving...

Remove the purge solenoid's tube from the front of the manifold and cap the port on the manifold, if this makes a difference then the problem is in the EVAP system.