I have my bike into Harley to try and figure out what is wrong with it.  Right during this year's Sturgis rally, I was unable to maintain a certain speed without it coughing/spitting/surging.  However, it's random.  It doesn't happen all the time.  We tried fuel booster & changed the spark plugs that they recommended.  It appeared to work for awhile.  After rally, I took it in for my 7500 mile maintenance and told them about my problem.  They did the maintenance and in addition changed the air filter which they said was pretty dirty.  Again, it appeared to work fine on my ride home.  But, then next time I went to ride, it did it again.  They have since hooked it up to the computer, downloaded whatever, changed the spark plugs and still nothing.  Any ideas?  

If this model has the fuel pump mounted in the gas tank have them check it to see if it has come loose. My partner had this happen on his Ultra Classic and was told it is a common problem.