Is my bike fit a problem, I'm experiencing achilles tendon pain?
The achilles pain and some tightness in the back of the calves comes from ankling too much, by pedaling high on the balls of your feet. I find that I do this when the seat is a bit too high.  Lowering the seat slightly and making sure my cleats are positioned more toward the center of my foot as opposed to toward the toes helped me to alleviate this.

Try to notice whether you are pushing with your ankles while pedaling, this is the motion that causes the stress on the tendon. I lowered my seat such that it didn't feel like I was overextending my leg during a pedal stroke or trying to tip/toe at the greatest point of extension. 

See sheldon for more info on pain in the tendon.

Related question on cleat postion:
Why not place the cleats further back on the foot?