2016 Gmc Sierra 5.3 p0308 on cylinder 8

My 21 yr old sons truck which luckily he bought an extended warranty on it has been in the dealership since the first of December. It had a collapsed lifter on cylinder 8 they said they replaced the camshaft and lifters to the tune of $6500.00. He got it home and 2 days later p0308 flashing again, I hooked up my MS 906 to check live data I noticed bank 2 o2 sensor that did not look very good and also the bank 2 cat was 50 degrees colder that bank 1. Is it possible they missed a bent or sticking valve, my son is very discouraged and I live in Indiana he's in Michigan. Any input would be greatly appreciated!

I wouldn't sweat the downstream O2's or cat temp differences right now. Neither of those by themselves is going to cause a severe misfire.

There are a couple quick checks your son could do if the misfire is constant. If he has an incandescent test light or a spark tester, he could check for spark at the #8 plug wire. He could also do a clear flood crank and listen for a low cylinder. But ultimately, I think your sons best move is going to get the truck back to the dealer for a recheck. Get a tow truck if the dealer is any significant distance away.

Thank you for your input he's fortunate he bought an extended warranty I just think the GM dealership mechanic isn't doing the proper diagnosis and my hands are tied due to the warranty. He did a wide open throttle and said it sounded a little different but my son's not a mechanic. I'm thinking maybe a bent valve or sticking valve guide possibly.

A compression test would prove it if that's the road you think you're going down.
Does he feel it misfire?
If it doesn't actually misfire but the CEL blinks, and since you have that nice Autel, you try a cam/crank profile relearn.
But, I agree with Tyler. The shop that did the work should be given the chance to check it out and make it right.