I have a 2011 sport unlimited 6 spd when I put it in reverse I get like a vibration in the clutch pedal when moving. If I have my trailer hooked up and try to back up a hill you have to work the clutch or it stalls and you can smell something burning but its not a clutch burning smell. Any ideas what this can be? Can the throw out bearing be causing this? Bad clutch? It only has 3600 miles on it and the trailer is just a 5x14.