Stereo Problem in my 54

[Handfull 54]

I just installed an Alpine 9886 stereo and a KTP 445 amp. The stereo plays fine when the truck is parked but the radio cuts out for a second several times when I'm driving,. The radio itself stays on just the music or voice cuts out. I am using two Alpine 5" speakers in the doors. I have 2 6x9 speakers for the back but have not hooked them up yet as I am getting the upholstery done soon. Any suggestions on where to start?. I wiggled all the wires while parked in the garage but it plays fine. Take it out and a block later it cuts out. I've hooked up several stereos in the past with no problems, so I'm a little puzzled this time. I have the antenna bolted to a bracket on the frame between the cab and the bed and a small foam ball on the antenna half way down the antenna so it won't hit the body. I am going to try a Cd next to elimenate the antenna. Thanks in advance for any help.

Dave in California