A lot of manufactures quote speeds with their lightest pellet under ideal circumstances, typical results with average pellets are commonly much lower. 900 fps with a mid weight, i.e. 8 grains, would be considered a good performing, "broken-in" rifle. I have mine soft tuned to shoot low 800's.
Having said that, most rifles of all brands benefit greatly from disassembly and tuning, your other option is to shoot the beejeezes out of it until it breaks in, 500-1000 pellets. I prefer the tune route myself.