From your original description of the problem, it sounds like the CG is too far aft. I wouldn't deviate from the manufacturer's specs for incidence and thrust line until the CG is located correctly. The first thing I'd try is to use a very reliable way to make sure the MAC is the correct length and it is located correctly. Next, locate the CG at 20% of the M.A.C with the incidences and thrust line set to specifications. It should fly a little nose-heavy but be very stable.
Next, check to see what % of MAC that the Mfgr recommended for a CG location. They or maybe you, have made a mistake there.
With the CG at 20% of MAC, see how it flies. If it is nose heavy, change the CG to 23 or 25 % of MAC and retest. Above 25%, move the CG aft in 1% increments until you get the performance you want. Caution: be sure to find the neutral point location before you go aft of the 25% of MAC point. For a better description of this, look at www.rcaeronauts.com.