If trim changes with airspeed, yes you need some adjustments. You did not say how it changed. If it climbs with increased speed or dives as you reduce power, you need more downthrust. If it is a roll rate change, you have a warped wing or two warped wings. Have you checked your relative incidence, i.e. upper wing relative to lower wing? In some dozen or more bipes I've built including two Phaeton40's and two Phaeton90's, all flew best with the upper wing 1.5 degrees less angle of attack than the lower wing was. As you change this relationship, you will find a definate difference in how well the plane handles through all manuevers.