Mike,

Theres another factor here that no one has mentioned DENSITY ALTITUDE! its summer time and its hot which raises the "Density Altitude" making your airplanes performance a lot less than it would be if it were cooler. In other words if your flying strip is at a 1000ft above sea level the effective altitude might be maybe say 3000' on very hot day. Density altitude effects performance drastically with full scale aircraft the same is true with models. Get a cool morning in the fall of the year you've got a lot more power. You may want to try a 10X5 pitch prop it may help, but only use full power for takeoffs and go arounds.

Heres a link that you can read about Density Altitude.......

http://www.mountainflying.com/densityalt.htm