GM-GMC: 2004 gmc 2500 failing to start, auto car starter, gmc dealers


Question
I have a 2004 gmc 2500 with a 2 way after market car starter in it.(not sure if related) Once in a while it won't start. It try's to for 5-10sec and stops and re-try's again.I have been told many different things including:
         -Bad Key, try getting a new key.This does not make sense because it won't start with the car starter either.
         -Faulty relay for auto car starter, Apparently the GMC need a relay installed to by pass the factory security auto diss abler.
         -Key barrel wore out, some resistor in there not working properly?
         -Need a new car starter
Not sure what I should do, don't really trust the GMC dealers in my area. My regular mechanic is very unsure. All car starter installers I have talked to want to install a new system. Please advise what you think?

Answer
the fact that it tries and wont start i would say that its not the key. common sense
the relay possibly and since it needed that to disable the security feature i would say that sounds suspect.
i wouldnt say the key barrel because it has nothing to do with the key
and as far as the car starter did you install it yourself or have it installed?
if you did it yourself it still should have some type of warranty, if someone installed it i would ask them or take it to them.

it is directly related to the car starter is my guess to be honest.