Chain slips/jumps occasionally (with all new parts)
a theory: you might have too much friction between the derailleur cable and its housing. such friction could prevent the chain from going to the intended place when you shift; when the friction subsides, the cable would move and the chain would slip into place. 

apply some lube to the cable and slide the housing back and forth to spread the lube along.  this could help if my theory is correct.