major misfires on a 5.3 help please!

[Yukonboy2014]

I have a '01 5.3 with 244k miles on it. Lately I've noticed that if I floor it, it knocks and rattles and looses power past 3500 rpm and shows the random misfire code. It had plugs 43k miles ago, and bank 1 oxygen sensor is dead downstream if that helps(that code came on a few months ago). Anything I should try/possible fixes before I take er to the dealer? Thanks