Yeah, the problem, as I see it, isn't that the PIC and your math is too slow...the problem is it's "too fast". This makes the ADC sample the signal very quickly so that between two samples the difference in altitude (or at least in the result given by the ADC) is so small that the actual change may drown in the noise. This fools the deployment algorithm into thinkin the altitude decreased.

When you introduce the PAUSE 200 the ADC only samples the signal 5 times per second (or there abouts) so the difference in signal from the pressure sensor is large enough not to allow the noise on the signal to trip the deployment algorithm.

There are several ways around this. The easiest is to do what you've done but tweak the PAUSE time to make sure the signal actually changes enough AND allow you to store enough samples depending on estimated time of flight. Another aproach might be to take 10 ADC samples and average them to filter the signal a bit, and then make sure that the a certain number of concecutive samples shows a decrease in height - not just one.

/Henrik.