I been having the same problem with my wind cruiser. Aside for the motor being intermittent, I couldn't get any altitude at all. It would maybe get to 20 to 30 feet and that was all. But I must say at about 30 feet the plane flew OK.

I kinda got sick of the rate of climb, so I changed the 6 cell into a 7 cell. I took all the shrink wrap off and install the 7th cell in front, right in the middle. the weight added was about 4oz. I added a little less than half of that to the tail and took it to the park...

It flew like a complete different plane. With Full throttle it took off like rocket and maitains level flight with a bit more than half throttle. The added weight didn't seem to affect it at all.

The ESC seems to take ok too.

I'm now thinking of sticking my micro servos and receiver in it so I can get get some v tail mixing so i can control the ascent and descent.