Any GM techs on here 6.0 v8

Have a 2005 Chevy 2500 with 6.0
37,000 miles on it
P0300 random missfire… mostly on #5 but see it on others too. Seems to act up mainly under load.
Compression test good
Swapped plugs, coil, injector…. Currently spraying intake gaskets to see if they are leaking

Any ideas on what to check?

Seen injector rails get clogged up w/ dirt...a lot of those don't have fuel filters.

Does that have AFM?

Get the cam sync signal reset/relearn .
Read here.

No, not in 2005. Came out in 2007