Mine is very stable at low speeds. I land with just a small amount of throttle. I suspect your engine incidence is wrong. If it climbs with power it might have up incidence. I set my CG so it flies hands off upside down. I fly with slight 1/16" spoilrons just to avoid wing rock in harriers.

First get the incidence correct. Test this by flying at mid power and trim it out, then fly at high power. The plane should track the same.

Next test CG, the inverted test is good, but you can also fly it high with mid power, then point the nose down to 45 degrees as the plane accelerates it should stay at 45 degrees. If it flattens out, you are nose heavy. If it dives, you are tail heavy.

Have faith, this is a good flying plane. stick with it.