Your rating in may was just inflated because of the various changes they had applied to TT then. The whole system was unstable for about two weeks, with the ratings of the puzzles themselves being insane. Most TT users reached a rating about 300 points avove their normal rating then.
So did I, which is why I reset my rating. - And now comes the funny part: I found out that it is way more satisfying and effective to reset one's rating every two weeks or so. Then I climb steadily again, strictly keeping my solution ratio above 80%, no matter how long I need for the puzzles. This is good to improve in accuracy. After a week or so I reach my limit then (currently about 1500), when I'm confronted with puzzle I need multiple minutes to solve (the above 1800 stuff), which why I can try/solve way fewer puzzles, and after a couple of days I realize that my pattern recognition abilities deteriorate significantly. This is when I reset my score to start all over with the quick-and-easy stuff.
I've done this 3 or 4 times now, and with each iteration my rating is about 50 points above the limit value of the previous iteration (like 1200->1400, reset, 1200->1450, reset, ...) . I get a very broad band of puzzle types and difficulties, and my rating is always rising, so there is much 'positive reenforcement' and no frustration.
Perhaps I should mention here that I started with chess only in march, things may be different for more the more experienced addicts.
Well after reaching over 2000 rating and puffing out my chest I got shoved off my high horse and landed all the way back to the 1200s.
Today I just broke 1400 and will let it rest for a day or so until my next level (1500).
Someone in another thread mentioned that you can game the TT system by not accepting (making) the first move on the difficult ones and only gain points on the sure things. I suppose that would work, but the program isn't called "Trainer" for nothing and by not taking the hits you will never see the path to the best move or learn from it.
One aspect of TT, I was impressed with, was the statistical matrix. It is so comprehensive, it had a tactic called "opposition", which in 20 years and several books on chess I had never heard the term before. Had to Google it.
Once I found out it was an end game tactic I realized why I did so poorly at it. I have played nothing but 1 minute for 20 years online.
My best performance was on "en passant", but whenever it presents itself I naturally assume that is the key move.
Curious as how how others use the Tactical Trainer.