If I'm not mistake you're using 1 hander nat slayer right? With nats ring and rorg? The problem is higher grift RG or elites HP scales really high when you're moving up grifts and elite damage bonus starts to really matter. Hence why sojs or unity especially is a must have. For 36 onwards i use unity as it halfs my damage when its equipped to my follower. Jailer eats only a quarter of my HP so its easily fully healed by my templar immediately and with leg gem 25% + 15% from my unity i have 40% bonus dmg vs elite. Also single wield damage range is too small unless your hitting 4.15 BP. If you're hitting 8m-10m frost arrow with 1h crossbow at 2.85 bp and bows are doing 15-20m  at the same bp, you might want to consider switching. I think understanding sentry mechanics is highly important if you want to have optimal dmg. There's a lot of info on DH thread and videos to go through to see how effective they are. If you scored a good a good high dps bow, WF, uskang, cluckeye or whatever, use it. It makes a huge difference.

GR level will depends more on your overall gear instead of bp bro.

to check bp

Character total ias X tnt ias

to check char ias, just open inventory window and expand the character stats. tnt ias is the legendary pet % stated.

for eg

1.93 (char ias) x 1.47 (tnt ias, 1.xx, replace xx with ur tnt pet ias value)=2.85ias or you can say 2.85bp

aiyo dunno that is clear onot 

sometimes in normal T6 rift, meet champion versin of Winged Assassins. They jail you and jump on you = 1 shot kill. (Coz normal T6 jailer won't 1 shot DH, but with Winged assassins yes)