Find someone that has another satellite antenna and cable and hook it up to your Sirius unit. You might have a bum antenna or cable. Also, check your cable routing -high frequency cabling is very intollerant of sharp bends or kinks. The ridges on the roof will not interfere with your antenna's ground plane.

Power,
10A is plenty for the Sirius tuner. I'd do a little research, but most likely it draws less than 2A. I highly recommend the add-a-circuit fuse taps, I use them all of the time (and it's doubtful that anyone's radios get beat up more than mine).