My '04 denali will not start consistently. after running hard for any period of time.

...I'm going to go ahead and say that it's the MAIN ground...the reason that I say this is your ignition relay is not gonna stay engaged if it's got only 10.5 volts to keep the contacts hangin' in there...so take the black battery cable, where it attaches to the chassis/ground and wirebrush the chassis and with a pliers hold the lug and wirebrush that too....you see what happens is the 300 or more AMPS requirement of the startermotor develops a layer of "semi-conductor" of the dis-similar metals in a firey-blue spark...okay for the first dozen times, but then the reduced voltage affects the delicate components...such as the ECU, ignition and fuel relays~

Thank you for the info! I am going to apply the recommendation tomorrow and will advise result.