In case anyone else has the problem, I found several things that solved my slow takeoffs.  I changed the aircraft.cfg file from N2 tach of 10095 rpm to 10300 but did not change the static thrust.  Then I recalibrated my joysticks (I use 2), and now I easily reach n1 tach of 106% and my 707 rotates and lifts off with a normal takeoff roll even with max payload and 99% fuel load.  I can hold 15 degree nose up pitch and still accellerate and hold normal climb rates.