amatuer point of view: 
if it pitches up, it looses speed > slowly pitches down > gains speed > pitches up again. 
so you have to use trim (which is a bit crude, no idea if its that crude irl) and throttle to maintain a neutral pitch. 
and just accept small changes in pitch up down and correct them yourself.   
just be happy its not a warbird with prop-torc :)