Q: trying to figure out misfire or fuel system problem

i have a 3rd engine mustang with around 140000k I believe and its losing power when I accelerate. It happens in all gears and at all speeds. And sometimes leaves me with a rough idle. It shakes and only seems to have maybe 30-40% of its normal power. It shakes and sputters I can feel it in the steering wheel. It also leaves an unburnt fuel smell when I get out. Sometimes puts out white smoke out the exhaust. Not heavy just a light amount. Sometimes while it is sputtering it will act like it caught the gear and will pick up like normal when I accelerate but after I let go of the pedal it sputters again. It will only happen maybe 1 out of every 50 times I press the pedal. I changed 7 of 8 spark plugs (a bolt for the cool was rounded off didn't have the socket for it) and no change. I turned off the fuel system from the trunk and let it die then turned it back on and that seemed to fix it! But then today (about 2 days later) it starts happening again.

My car has 140000 miles.
My car has an automatic transmission.