I hit a 1400 plateau as well, number of ways to break it.
1. I am almost positive you are not calculating 6 ply every check capture and major threats. Good news is the better you get this actually doesnt seem to be something you always have to do. The best players eventually know automaticly what is worth spending there energy on.
2. There are some tactics that you are especially bad at. Go through your games to see what they are. Just seeing what you miss often should hugely improve results. When I was a 1300 I missed tons of pawn forks, 1400 I had a propensity to have my rooks skewered, I still miss queen forks a couple ply deep. Everyone is different but there are tactics that you are missing that other 1400s can spot quite quickly,
On the flip side there may even be tatics you find you are really good at for your level. I was pretty good at seeing and using long diagonal bishop threats for a 1300, at 1400 I think noticing where the knights wanted to go helped my results.
3. 1400 do not seem to understand pawn breaks, some do, many do not. Read up on pawn breaks if you do not understand them well.
4. This is weird but those times you cannot play chess and have nothing better to do work on visualizing the large center from both sides of the board. e4 e5 d4 d5 c3 f3 c6 f6 e3 e6 d3 d6 c4 c5 f4 f5. I still cannot perfectly see them in my minds eye but I am getting close. Yes it is boring but I truly think it helps.
I have been playing chess for about 2 months now and have been playing purely off of my own skills.
I seem to have hit a plateau around the 1400 rating and wish to improve my skills.
Sorry if this seems over-generalized, thanks in advance.