My 07 Ultra Classic suddenly started misfiring at low rpm. It was running fine and I pulled into a rest area for 30 minutes. I came out and on excelerating to get back on the highway it stumbled as though running out of gas. I down shifted and it took off again. I found that if I kept the rpm above 3000 it ran flawlessly. It only misses fires at low rpm and at idle it will run on one cylinder. Got any ideas? Or has anyone else had this problem. PS I have changed spark plugs and replaced the fuel pump line in the tank as suggested, no help.