03 chevy 1500 wont start?

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"Won't start" is a rather vague and unspecific statement. 

To get a spark, the starter must be turning the crankshaft, so why did you change the starter? 

You need fuel.

Is there fuel pressure?

Did the timing belt snap?

Pulling a plug wire is as FAR as I would go. If there is a spark then it is something else.  

. The next check is "Is it getting fuel"?  I would pour about a cup of gas into the intake,(how you get that cup is you figuring it out) & then get in the car and put the pedal to the floor because you know it has too much fuel so you need to dry it out and turn the key to crank the motor over. It will start up for a minute or two and either stay running or DIE.  If it dies, then you know it ain't getting fuel.  Check the fuel gauge.  Then go and take the gas cap off and put back on again in case there was a vacuum.  See if the car starts.  If it does now, then you know that the fuel pump is getting weak.  That needs replacing.  Maybe you can get the car home, or you TOW IT.

Fuel pump is probably in the tank...so a "shop job"

If the motor is turning over why would you replace the starter?!  If the motor cranks over the starter is working. If you have spark the next thing you do is determine if you have fuel. Spray a shot of starting fluid into the throttle body after taking the air cleaner tube off of the throttle body. If it starts and runs for a few seconds you need a fuel pump.

It ain't got no gas in it.

mmm hmmm

Spray starting fluid on the intake and try to start.  Truck starts and dies, fuel pump could be bad.  Check fuel pressure while cranking with a gauge.  Fuel pressure is zero, fuel pump fuse, fuel pump relay, fuel pump could be bad or there is a wiring issue.  Good luck.

If it's a Vortec a common problem would be low fuel pressure