ive got a 2003 5.3 flex fuel suburban with a bully dog gt tuner. problem started about 3 weeks ago. the truck would shut off occasionally at stop lights with no "stumbling or miss fire". then it proceeded to start dieing while driving, just shut off with no stubling or hesitations. i thought fuel filter, replaced it, it was dirty, then replaced it again about 1 week later. problem went away for a few days. then the same thing started happening again. i returned the engine tune back to stock. i pulled the injectors, fuel rails and throttle body and checked / cleaned everything. problem was gone for 2 days. it started dieing again today so i dropped the tank and checked the screen, its perfectly clean, pump was replaced about 9 months ago. went out this afternoon and it wont start at all. 50 psi at the fuel rail, but now no spark to any of the di coils. i tested both the cam and crank sensors and they are functioning properly also i disconneted the mass air flow and checked all the fuses. still no start. during all of this i have not gotten any trouble codes.

before this problem it was running great. plenty of power and getting 26mpg on the highway with the mods i have done.

 

Welcome to the forum.

Might try uninstalling the Bullydog first. I doubt that is causing the problem but it gets rid of one variable.