You are about 5 11 can i ride a XL gt avalanche 3.0 mountain bike?

XL doesn't say that much, it'd have been better if you'd stated a frame size. In terms of rideability, it's a sliding scale. You will be able to ride it. but it might still be a poor fit. My advise would be that you do a net search for "bicycle fitting", then have someone help you out with a tape measure and see what the formulas will recommend. Do at least two different and pick something inbetween.