Right now I'm using almost the same spec:
Pistol + Shield
15 Slashing Wounds
15 Lightning Tree
15 Nature's Blessing
15 Gift of Renewal (very awesome with Closure)
13 Storm Front
1 Old Growth
1 Storm Warning
15 ? <<<< This is a big problem right now since I really dont know what to take here. I tried Breathingroom which I don't like this much coz of the animation, Tree of Life is okayish for the reg BUT it takes like years until it has grown to start healing u which is for lategame raiding crucial. Lightning Strike doesn't overall convince me for the flat DMG. Giant Killer is meeeh somehow, Nature's Rage and Vengeance are IMO not needed and not worthy thought I don't underestimate their usefullness they both don't really contribute anything REALLY special to the build, same as Tree of Roots. I'm testing ATM Storm Surge which is IMO the best way to go. It synergizes very well with Storm Warning and Storm Front and since most of this build is lightning based the +20% bonus to lightning dmg can help a lot! Furthermore it does have a fast cast time and animation which is okay.
Any ideas or experiences are appreciated!