I agree with what has been said, The 55-300 does not cut it for indoor basketball. Also lighting in gyms can vary greatly. Some like the one I have shot, have terrible lighting. You can (if given permission) place wireless bounce flash in the corners to help bump the ambient light, Direct flash can annoy players and refs.
I have attempted indoor basketball with the K-7 and Sigma 70-200 F2.8 /FA 77 1.8LTD and it was still
very difficult. ISO 1600 was the highest I wanted to push the K-7 so technique and timing was of ut-most importance. Time the action where the movement is slower. Ie instead of shooting as they jump, shoot when they hit the top of their jump, or instead of shooting as they run up the court shoot when they player hesitates or makes a cross over move.
I have since bought a K-5 which has MUCH better high ISO performance so life will be a touch easier. Your K-x would fit somewhere in-between the K-7 and K-5 in terms of high ISO. But still, In my experience you need lenses with F2.8 or faster.
A couple of the shots from that game.