I've done 15,000' with stock P4 controller using windsurfer. That test had full signal bars the whole flight. That's using ch20 and 4mbps bitrate.All you have shown is that it was a bad investment for you, and you did the installation, so whose fault are the bad results? I got 5.8 miles of range control on my P4 last night to 51% remaining battery on my DBS-02 mod with boosters attached on a GL300A controller. Without the boosters on the same transmitter mod, I got 12,500 feet. With just a windsurfer and the stock P4 crappy transmitter, I got 6,700 feet. Without the windsurfer, I get 2,500 feet! Those are my results!
However, I've noticed my P4 can be temperamental, losing full contact with moderate clear view distances that my P3P would be rock solid, 3000 to 4000' range