clutch problem need help

[waterjockey20]

i have a 2007 350 crew short bed with manual trans. the problem im having is the clutch has intermitent softness. it sticks then hits your foot sometimes when down stifting. i have replaced the plastic bushing on the rod to the pedal. when i use the truck to pull my gooseneck or plow snow the clutch seems to get better and works like it use to for a while then back to soft pedal feel. any help would be great. thanks