Hey Aztec,
Good choice on the bike.
Here’s some ideas, although impossible to diagnose and fix over the INternet.
First of all, look at yourself in mirror. Notice the position and posture of your shoulders, their relationship to you neck, the angulation and tonus of your musculature where your arms leave your shoulders. Get a good mental picture of that in your mind.
Good.
Now.
Get on your P2K. Use a mirror or, perhaps even more dramatic, do this: Get in the aero position. now. from the chest up, freeze! Hold that posture. Don’t move. Now, I know this is hoaky, but hold that posture from the chest up and then sit upright on the bike.
OK.
Is this upper body posture natural? It is similar to your posture on the bike? No, it isn’t is it?
Now, let me guess… When you looked in the mirror your shoulders were about six inches below your ears. Now, your shoulder are only three inches below your ears, your shoulders are hunched upward and rolled inward I wager. There- that is a contributing problem (guessing here…).
OK, you need to obtain that more natural posture you saw in the mirror but now on the aero bars. Maybe a slightly shorter, higher stem, extra spacer and slightly wider elbow pads. Again, just guessing, but that may either be a good temporary solution or even a permanent one. give it a try.
The seat, well, remember, the angle of the seat is important, and the saddle pad is a good idea. Try making sure the front portion of the saddle- just the nose- is parallel to the ground. The Alliante you are using has a lot of “rocker” or curvature as viewed from the side. Not too good in the triathlon posture.
If the Alliante with the saddle pad and a level nose doesn’t get 'er done then try another saddle that has a more padded nose and a flatter profile. I have great luck with the Arione Tri saddle.
Good luck my friend…!