do you do upper body workouts?
It could be that you have too much weight on your arms for your core strength, which is causing your muscles around the shoulder and neck to tense up.
to take off weight from your arms, you have to slide the saddle back and get a shorter stem.
since you have another bike to compare fit, line them up at the BB and compare the saddle and bar positions relative to the BB.
The only workout i do is cycling. I very rarely do anything else unless it's just lifting stuff working on my truck or something. I thought about the stem. I looked up a while back and they mentioned when sitting your stem should hide your front hub from view and my stem is further out so i can see my hub behind it. I'm looking to upgrade to a carbon stem anyways so i can just order it a little shorter than my current stem.