The only thing i would change with ur build is move the 1 point in Percurssive Shot (the knockback on aimed shot), Since u said this is mainly got PvE bosses are not affected by knockbacks, i would put that point into Stay Low The increased hunker down by 3 secs and hightail puts u in hunker down for 3 secs. The reason for this is there are a lot of bosses that knockback or pull in or do something that hunker down negates. The second thing i would do is move the 2 points in Kneecappin' (the increased duration on trauma and leg shot immobilize) into Heads Up (Speed boost after hunker down ends). The reason for this is the same as before... Trauma and leg shot have no affect on ops bosses and the increased speed even applies to the hunker down u get after using high tail it so it makes a very immobile a bit more so. Your original skills help when dealing with trash im sure but you want to maximize your dps and effectiveness on bosses. And i mainly run dirty fighting and didnt have much issue with styrak on Hm... i even beat the SS slinger what was in the same fight. However SS does have much much more burst which is good for a lot of fights. I just personally like the DF rotation and play style better