Decent in all variants of chess except in 3checks, what should I improve to increase it?

My elo increases every week, my tactics are now 1800+, I keep working them and lessons and yet ... 3 checks is my lowest elo, what weaknesses should I work more ?

Thanks in advance for constructive advices.

You should post some of your 3 check games so that people can analyze them.

lost on time and felt i kind of lost tempo

 If you play 1800, you quickly achievebale potential level in all variants goes around 1800 too. This may include short theory study (about 100 games) in each variant. It's not the best idea to say this, but chess.com have terrible instruments to improve variants play. No theory, no analysis, variants selection is rather small.

To think of 3-checks, it's highly computational variant and relates to your playing style a lot. If you combination player with sacrifices, it will help. Second element of almost all variants is debut study. Atomic chess are full of debut traps, horde has very beautiful intro theory, etc etc, and  3-check is even more sensitive. Very strict opening theory, most of games white attacks ke4 and black's best idea is Kingf8. Also it is one of smallest variation variants, because most of positions have direct win for one of sides.

Oh and main rule of any improvement (which nobody uses ) - to play only long (like 30+ min) games 

Responr to Nelson below: playing vs computer is far from necessary, but playing vs much stronger enemies IS necessary. Bad side is that high rated players want to play even more high rated, not you .

Thanks for the hints @Oledgy and @NelsonMoore!

I will practice more variants and will try the suggestions, also will attempt to play longer games, which I thought recently i have to do now in std chess as well to keep progressing anyway.

Yeah chess.com is terrible with variant support