Stuck around 2000 rating. Concrete advice for improving? I've been stuck around the 2000 rating mark on various different online chess websites for a few years now. I seem to have hit a wall. I'm quite busy so when I do find time for chess I tend to just play some blitz for enjoyment. But I suspect that is what is stalling my game. I've decided to spend more time studying than playing in order to finally progress further.   

I am looking for concrete advice on what other players have found successful in their own experience of going past 2000. I've just ordered Dvoretsky's Endgame Manual and I plan to study several key positions each week over the next year. I hope that improving my endgame will bring my overall game up. But I'd be interested to hear other ideas too.
Without actually knowing your strengths and weaknesses, I'd suggest doing the following:

Studying endgames is a great idea - it will help you to convert equal positions into wins against players with worse endgame knowledge. However - an equal position has to be reached first.

Find out what style of play you excel in - and learn how to get into positions that fit that style. The most drastic example of this might be the Fried Liver Attack. An engine really doesn't mind playing black here (I mean - it's a free knight!), but human players, even Grandmasters, are just screwed; they are just not able to calculate a complicated position like that well enough.
Improving here starts with analyzing openings and getting a feeling for positions, the weaknesses and strengths they bare and what long-term consequences your moves make. Aim to always know why you make a move. To practice this, you take any position, make out weak and strong points and formulate a plan for both sides - then think about moves you want to play to pursue your plan - and delay your opponents plans. Bonus points for moves that do both.
Take your time for this - it will help you find a plan OTB if you practice it.

At higher ratings games are usually decided by strategy, not tactics. While it is important to have a good eye for tactics, tactical opportunities will be rarer and rarer. Get a good position, keep a good position and the checkmate will come naturally! :)