The Press and Balance?

[Notorious]

For some reason when I do the press, I have trouble keeping my balance in the lockout position (bar directly over shoulders, head forward, upper back shrugged, abs and glutes tight). I think it is preventing me from moving the bar in a completely straight upward motion.

Right now my 5RM is 117.5. However, I tried just holding the unloaded bar in position and I was still shaky as hell. Sometimes I have the same problem as I unrack the bar for bench press.

No caffeine or any other stimulants whatsoever in my diet, although I will admit I can't ever really hold my hands completely still. I think I have decently flexible shoulders as well (I was doing shoulder dislocates the other day and people were commenting like I was crazy).

Is there a fix to this problem? Could it be some muscle imbalance?

Other 5RMs are:
Bench-155
Squat-205
Deadlift-310
I can probably only do like 7 BW pull-ups (with a BW of ~165).

[Mark Rippetoe]

I need to see a video.