Hey, I don't seem to have much trouble playing solos low down on the fret bored, but anything up higher then the 12th fret, i start having trouble, my fingers have trouble hitting the right frets and the overall sound is really bad, almost like the strings are being slightly muted? any tips or ideas to help would be much appriciated
slow everything down and gradually increase the speed. use a metronome.

you could also improvise over some backing tracks if you start waning interest. improvise past the 12th at a speed comfortable to you (a speed where you are in complete control) and naturally over time your fingers will speed up.