Backfire on deceleration?

So ive been running my 2000 5.9 magnum efi swap for about 6mo and i recently started getting backfires on deceleration..
Ive been reading on a causes of this..
Exhaust leaks seem to be one reason
And running lean another..

So my question is would a Exhaust leak near the header make it backfire
So badly near the muffler or should i start diagnosing at the fuel system
Seems to be drivers side only