stalling on 2001 GMC Yukon XL Denali

when i step on gas pedal a lilttle bit then let off the lights go dim an idle goes down for a few seconds which cause my truck to stall when waiting at stop light or backing up I changed spark plugs and wires ,battery,alternator and the fuel filter what could this be thats making it cut out like that???

3 answers
take the air intake tube off the throttle body and clean all the black stuff on the walls of the intake, push the flap up and clean behind it as best you can just clean whatever black stuff you see in there and be sure to use a lint free cloth and carburetor and or throttle body cleaner
Your vehicle has On Board Diagnostics 2 (OBD2), attaching a scan tool to the diagnostic socket under the dash may show codes or pending codes that may give clues to what the problem is. Stalling could be caused by poor electrical connections, a vacuum leak, or a failing idle air control valve. A good professional grade quality scan tool has diagnostic features that may help diagnose the problem.
sounds like the manifold gasket.