Low light, indoor, action shots.....help pls

Hi, I have a Rebel T1i for a year and my outside sport shorts are great....I'm trying to get better at shooting low llight indoor arena action shots of the equestian jumpers at our local barn.  I've upgraded this past christmas to a Canon EF 70-200mm f/2.8 L USM lens because my research said it was amazing at low light conditions.

I've done the youtube and other sites to learn more but it's not really falling into place.  last week I got some decent shots at a M f/2.8, iso 1600, 1/125, but then I get home and am dissapointed in their sharpness.  I understand the basics of each of these settings but how does one go about blending them to produce the sharp clear pictures when they are moving.

I have been working on my panning techniques.....but I'm frustrated, I guess I kind of thought that this new lens would help me out more and it's not.

I've also tried the AV and T modes, even with an exposure of +2.

Please any suggestions would be appreciated!!