Welcome to JustAnswer, I'm Neal and I am here to assist you. Please feel free to ask follow up questions, it is part of the process.
There is no way to tell, they used the same block and heads so the casting numbers will not help. Your best bet is to see if you can get the vin number from the truck it came out of.
Other than that you couold pull the pan and get the casting number off the crank.
But the easy way, if you are used to your truck, there is enough difference in power that you should be able to tell if you now have the different displacement engine.
The mileage should have been better if you went from a 5.3 to a 4.8. But with the big tires I can't say for sure.
No other codes?
I would get it back to the shop that installed it see what is wrong.
Is the engine under warranty?
That is a great warranty.
That code for a low circuit for the knoch sensor is going to be a bad sensor or damaged wiring. And it will cause a loss of power like he said.
The book calls for 2.7 hours
It does require removal of the intake. Not that hard but time consuming.