My dad has a 04 silverado v8.We replaced the ignition switch.Maybe it didn't need it.I will start from square one.His truck died while going to work,65mi drive.Had his friend get some gas and it still wouldn't start.Onley guages that worked was the gas(onley when it got low),temp,oil,& batt.Has been like that for a long time.He thought maybe the gas meter went out.He took it to a shop.All they did was spray some starter fluid somewhere.It started,dad came to get it.He got about 10mi from home and it died yet again.Had it towed to the house.We checked 3 of the right side coils,none of them had any spark.Was holding them 1/2" or less away.Checked the valve stem up by the top left side of engine,gas comes out.So the pump is working and you can hear the pump when an attempt to start is made.Before we replaced the ignition switch,it would turn the belt with ease.Batt was freshly and fully charged.After replacing the ignition switch,belt doesn't even turn at all.And the key does not spring back like it should after in the start postion.Batt is fine and has plenty of juice.I believe since we changed the ignition switch,maybe it set the anti theft or passlock on or something.Neither of us know what to do now.It was the right kind.Went right in,plug cable and box snaped in place.
I will try to provide more info if needed.Thank you all for any help/advice!We want to avoid taking it to the dealer.He has had it for 4yrs now I believe,no warranty.He got a 1,000 loan and that is pretty much the budget.

 

Sounds like you have multiple issues. I would get the ignition switch working first. It should spring back. The passlock system will allow the truck to turn over just fine, but just won't start.
If the shop your dad took it to sprayed starting fluid in it and it started I would be looking at a fuel issue. Just because you hear the pump and there is gas at the pressure check valve doesn't mean it is supplying the proper pressure. These truck run at a very high pressure (around 60 PSI give or take a few pounds). Get a pressure gauge on it and make sure that is what you are getting.

 

Ill see if he left his truck keys here at home.If so I will try to get the ignition going.Problem is the teeth on the original was moved,so we was playing a guessing game trying to find the sweet spot.After 5 failed attemps,he got the ignition switch out still pluged up,hooked the battery backup,& was moving the teeth by hand.Would not turn still.lights in the dash,stereo,and headlights would come on.But it wouldn't turnover at all.Not even a nudge.Hooked up the OEM ignition and same thing still.Do you know what would cause it not to even turn a lil?

We went to autozone,told them the exact silverado he has.And they gave him this one.
BWD CS643 - Ignition Starter Switch 2003 GMC Sierra 1500 | O'Reilly Auto Parts

Here is instructions we used to replace it.Pretty much exactly the same in the silverado.
How to replace your ignition switch (pics) - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum

 

If by chance you broke the passlock wire (two tiny orange wires) or fuddled up its connector which is pretty easy to do, it won't start. I might be wrong but easy to check and a pretty common gm issue.

 

I found a very easy way to set the ignition gear right.Installed the new one.Recharged the batt.Cranks good and strong,won't start still though.I told him he would probably need a new ignition switch soon anyway,has 128,147mi on the truck.He drives 950mi a month for work alone.But I think he is going to take it back anyway.Checked the orange wires,no damage.My dad said the mechanic did check valve when it was their and it was 50psi.
I went under the truck and looked real good.I think a gasket/seal went bad on the transmission,can see pink fluid all around it and black bar below it has a thin wet film of it on it.I don't think it would prevent the truck from starting,but thats the onley obvious thing I seen wrong.Its a very slow leak.