GWS Pico Stick help!!!!
Let me tell you what happened with my Multiplex Lupo. I flew it for the first time indoors in a local sports hall, and it was fine, if anything it had a tendency to climb like crazy at full throttle. I packed away at the end of the evening well satisfied.
A week later, and I was up at the field, in some nice calm weather, so in between glow flights, I thought I would try the Lupo. It wouldn't ROG and from a hand launch, even at full power, it would just sag and descend to the ground in a mushy semi stall. What the h*ll was wrong? I had removed the prop to lubricate the gears with some fluorosilicone grease, and on replacing the prop, I had put it on backwards. A quick bit of spanner work in the pits, and the performance was transformed.
I'm not saying that this is your problem, but it sounds awfully familiar.