truck wont start

Try ignition switch first.  Chevy uses a system called passkey and it sucks.  There's a magnet in the tumbler and it has to line up with a switch on the housing. They get worn out pretty quick.  You can replace the key tumbler first and that might fix it.  Hope this helps.  Good luck.

well im gonna go try out the ignition and ecm today, wish me luck

this is a very very rare occurance but i worked on a ford expedition and it was doing the same thing,  and everything we checked led up to a computer but we changed it and nothing fixed it,  we had the car for like 8 months then finally we found a piece of tin foil (aluminum foil whatever you call it lol)  on the inside of the crank pulley and every time the foil passed by the crank sensor it was reflecting the signal showing that the engine wasn't turning over.  when we pulled it out,  the car fired right up and ran perfect lol.  he must of picked it up while riding down the road lol.