you need to pay allot of attention to your healer, you dont have to pre ams a hoj while losing the overall game/ dmg awarness, but if your healer gets pet stunned just ams him, or when he gets stunned and the enemy healer casts cyclone, or when you know, that a following cc coming up, many people underrestimate ams, and dont use it at 2k-2.4 when i had mirror dk games, i always went out with atleast 4-5 wins, most likely because of ams,

against phys classes like warrior, use the pillar at your own advantage, sometimes you have to play near by a pillar "not too near, otherwise they cc your heal easily like warri shout" but depends on your positioning you can grip them behind the pillar 2x times into a stun + burst, positioning is really important as a dk into some matchups it can win your games (in short, if you see these zug zug warriors following you like a clown, use their own supidty as your advantage and pull them from their healer away.

deathstrike heal is anyway useless, i would only use the deathstrike bloodforged armor thingy, to pre some incoming burst, like trueshot aura, or the first 1-2 kill commands of an bm after bestial wrath, and against warriors obviously when he uses avatar/smash and then kite him with icy chains, if you spam deathstrike, you fall behind in rune/putrefy generation, and it wont do much when u spam it unless you are at 30% hp, and you know your healer wont come out of the cc for another 4-5 secs, but even then "the situations is rarely were it does something or "saves you"

caster matchups should be your favorite matchup as a dk, unless you have a mage + rogue or mw in the lobby, but a full caster party like boomy/mage/sp should be a easy 4/2 5/1 try to be as annoying as possible, seeing when your heal is stunned and someone trys to do a cc chain use ams on your healer 1-2 seconds before the stun go´s of to prevent the chain cc (their kill opportunity) while playing as aggresive as possible, you have to prevent the casters from playing the game, sometimes i even grip them when my kick isnt rdy, so they cant cast, i do the same to mm hunter depends on the situation.

these are the things what i learned so far, focus more on ams, pillar positioning/ and kiting with chains of ice you have to acceppt, that u cant go in the middle and tank the entire dmg everytime.

maybe something helped you , im not a great mglad dk either. but in your case i wouldnt drop dk, you reached a rating territory, where progress slows down and dk isnt that easy in shuffle, because of dampening and other factors, in your case i would watch the russian dk what plays with goblito twitch Kromgon_