My company work truck, 6.0 LS powered. A week ago, it wouldn't start. Boss had it towed to his preferred shop, personally, I think they're rip off artists! According to them, the crank position sensor "melted". IDK how hard it is to replace, but they charged him $700! As I was leaving, one of their techs waved me over. He asked if I had to turn the key on & off to get it to start. I said it'* never done that, he said "well it'* been doing it for us, and means the fuel pump is on it'* way out." Sounds fishy to me, and I wonder what they did to make that happen, because now it does take a second try to start sometimes! I also turned the key on, and waited a couple seconds, in case the pump needed to 'catch up'. But it didn't make a difference. I also asked a coworker who owns a similar aged GMC, with the smaller LS. He said the pumps do get weak, and he tested w/a pressure gauge, and it was below spec, but still starts & drives fine. Thoughts?

You need a new pump. It may leave you stranded.

The crank position sensor is trapped behind the starter. It'* not a $700.00 job, but probably a good $350.00 job, unless there are complications. I can't imagine how it would melt where it is . . . without other stuff melting as well.

Fuel pumps get weak on everything at one time or another.

When you say "it does take a second try to start sometimes", are you saying you have to crank it for a bit, turn the ignition off, turn it back on, then crank it again? If so, it might be just the relay.
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Basically, I turn the key, it cranks, then automatically stops. I don't turn it off, just crank again, and it starts right up.

I would replace the fuel pump relay first, see if that fixes it. $10.00 + 10 minute gamble.