My guess is that you are missing some errors of the people near your ratings, and against higher-rated people you are more aggressive because you need to be aggressive to win.
Can you show us a game or two for an example? Also, Live or Correspondence?
Everyone has their strengths and weaknesses. Some opponents that are "weaker than you" will be better in certain aspects(as you mentioned strategy etc). Maybe it is endgame play. One of the ways to move up is to be able to steer play into a game that you are more comfortable than your opponent in. Maybe this means getting real comfortable in a specific opening. Maybe this means getting a lot better strategically or in endgames etc. Lots of random ideas. But, I hope it helps.
Why do I have horrible problems against some people close to and below my rating and consistantly beat or trouble others ranked well above me?
I know it's partly to do with my preferance for tactics and therefore opposition who will allow the board to open up, but as i strive to improve my strategic game ive noticed there's just a way some people go about their build up that messes with me...
any suggestions?