I've managed to get a linear ramp-up frequency which is fed into a panasonic servo amplifier. My only problem now is that the ramp is so steep & changing the number of pulses does not reduce the steep
Is it that the motor can not keep up? or what.

things
1) "changing the number of pulses does not reduce the steep" changing the number of pulses should increase the "width of the step" does your scope show that you get the number you expect?
2) in one 'experience' I found that making the "step width" a function only of "number of pulses" made the motor stall, but making the "step width" a mixture of time and pulse count made it accellerate smoothly. The need for this would show by a good motor accelleration to a relatively high speed and then a stall.
3) it seems that you do far too much in the ISR, can you move something out
4) do you have other interrupts enabled
5) which processor, which cloks

Erik