It's really hard to say trying to visualize, not seeing the plane in person. But yeah it's a high possibility that the plane could be tail or nose heavy, but usually that's obvious. But I'd first check the throws. And see if you're getting enough or recommended throws in your elevator. I had this problem with my Wattage Mad Max. It seemed nose heavy, but I barely had movement in the elevator because of play in the control horns and pushrods. You may also want to get rid of that slow flyer prop if you're using that Himax brushless engine. Try maybe an 8x4.5 composite prop, and be sure it is balanced correctly. At our local flying field that's a big problem for beginners, prop not being properly balanced. See that there is no vibration, or funny noises from the engine. Lastly if you are sure the engine is operating correctly at full rpm's, check the tail fin, stablizer, rudder and wing proportion and see that it is all aligned straight and not crooked.

Goodluck