I know this reply is a little late, but just got my Pilot 87" extra 260 going. Mine was doing the exact same thing. Level upright flight with power it would dive, level inverted with power would climb. If I added enough trim for level flight, it would climb and stall when i let off on the power. So i added a rediculous amount of up thrust, planning on having to remove some, and was suprised it did nothing at all. So I tried a vertical downline with no power, and it still coupled to the belly. On the way home, I stopped and bought an incidence meter. Wings were nice and 0. Right stab leading edge was up 2 full degrees, and left was down a little over a degree. This actually equates to alot of elevator deflection. Relocated left and right stabs to 0 with the wings, and put engine thrustline backto 0, with the 2 degrees right of course. Hope to fly it this week, but alot of rain forcast here right now. I am certain it is fixed though. Flew it enough to tell its going to be an awesome plane. Will definately check this right off the bat on all planes now before I even start to build, much easier fix at that point.