If you replaced the cable then I would still suspect a problem with the antenna and or mount. You might try switching out a radio with a friend and try again.
Im running 20ft of RG58 cable from Radio Shack, a cheap uniden from wal-mart, and 108" whip. My SWR's are 1.2 on channel 20. I can talk from South Bay in San Diego to Miramar (about 20 miles) on a good day. And thats with the antenna down as in pic.