Im a level 87 Ranger but can barely take out tier 4 maps, what am I doing wrong?

So I have kinda ok gear, and followed a build where I had to do a little tweaking to not die as easily, yet I am still only safezoned in tier 3 maps.

When I run around in t4 maps I can easily get one shot, which sucks considering how little XP I get there.

What am I doing wrong? How to tweak my character to do better?

You'll have to be a bit more specific. What build are you using?

The most important thing is having 75% (or more with +max resistance gear) elemental resistance in all resistances. Also important is life: for mapping you'll probably have 3000+, but seeing you're level 87 you should have somewhere between 4000-6000 as a ranger.

Having some linked sockets with cast when damage taken + immortal call (and then maybe something like temporal chains/enfeeble and vortex/artic breath) helps. Make sure the gems aren't too high level compared to the cast when damage taken or else they won't activate.

I don't know what flask you're using. Do you have instant healing flasks? Do you have bleed and freeze immunity (super important to have that on flasks or somewhere else). Do you have defensive flasks like jade or basalt?

Are you using any auras? Consider switching to a defensive one like Artic Armor or Enfeeble (using that gem that let you use curses as auras that I can't remember the name of).

Have you picked up acrobatics or another defensive node in your skill tree? Do you make sure to not run into mob packs? Do you have a golem or something?

Looking at your character the biggest thing is you have 0 support gems connected to your skills, if you're a toxic rain build, having it in a 3G bow with Grace and another skill is gonna fuck you over royally. I'd heavily suggest looking at any toxic rain build for what links you need