Ok guys, I need your knowledge here. I'm having an issue starting (kind of) with my silverado.
Back story: 2006 Silverado 2500HD 6.0 gas 4x4 The block had cracked and I had a motor put in it with 106k miles 1 year unlimited mileage warranty. Truck runs great and has no issues with power or noises or anything. However, like every other time I go to start it, it wont start on first try, then second try it fires right up every time. Now I have tried leaving the key on for 5 seconds and makes no difference. Does it hot or cold, but doesn't always do it. Eample: this morning we left for work I turned the key fired right up. Drove an hour and got breakfast then went to start it and had to do it twice. It's just annoying as fuck more than anything. It has 52 lbs of fuel pressure so its not that I dont think.

52 seems lowish for a 6.0 from what remember tho.

52 is from the pump when you turn the key, I don't know what it is running, he just told me what it was when they tested it. I just put a new fuel pump in it too and it runs fine doesn't miss or knock or tick or anything. The diagnostic guy said it had plenty of pressure even when he was bleeding it off.

Should be 58psi but it should start on 45+. I'd need to scan it. Check the throttle body. Unplug the MAF and drive it. See if it still does it.

It had a bad MAF, it has a brand new one in it now, one I bought was throwing codes so I replaced it. It's not throwing any codes at all. I cleaned the throttle body a week before it went into the shop, and put a brand new TPS on it as well.

Did you do an idle relearn when you changed the TPS? Was it an AC DELCO tps? The throttle body is a sensitive area on these trucks.

You could also have a vacuum leak, bad coil pack, etc. I'd need to scan it to view the fuel trims. A quick way to tell is to unhook the battery for 30 minutes. Start it up without touching the throttle and let it idle from cold to full temp. Block the wheels and put it in drive. Let it sit that way for another 5 minutes. That should relearn the idle. If it runs like complete shit when you first crank it up after reconnecting the battery then you have a vacuum leak, or exhaust leak causing an O2 sensor to add or subtract fuel. Once the fuel trims adjust for it the thing will run fine but the problem is still there.