2000 Yukon Intermittent No Start

i have a 2000 yukon i bought used,but occasionally it will not start.some-
times it won't start on the first try of the day,and other times it will not
restart after it has been driven.the engine turns over,but will not catch.
i'm thinking there maybe a problem with the security system or the pass
lock system.i think that,because if i let the truck sit for about 5 to 7
minutes,it will start right up.is this a problem with the keys or the ignition
cylinder itself,or something else altogether?.....any ideas???

If this is happening in extremely cold weather, it could be a problem in the ignition switch. I have a 2000 Yukon/XL that I purchased new and this was a problem on mine from day one. In extremely cold weather, I couldn't start the engine. I determined that the problem was a defect in the ignition switch, where the contacts for the fuel pump became "un-made" when the switch is turned as far as it will go while cranking. I found that if I only turned the switch just enough to engage the starter, the engine always fired up. I decided to live with this "quirk" instead of having my incompetent dealer start tearing apart my new truck. This "Defect" only shows up in cold weather, apparently because the engine will start ok even with the fuel pump dropping out for a second or two during cranking in warmer conditions.