the resolution have no impact on the sharpness of the picture. could you upload a sample image?
are all images "dull"?
cleaning the lens inside or outside??
a dlsr works different than a compact camera - one of the main differences of the picture is the blur - or better - the [http://en.wikipedia.org/wiki/Bokeh|bokeh (click)].
what lens are you using? maybe the lens has a front- or backfocus!
you can use the fosus test chart to find out if your lens has this issue: [http://focustestchart.com/|CLICK]