> Are there any clever tricks that can slow it down to about a 17ms

No, I don't think so, you'll probably have to use the timer(s) or s/w. Like
MR-J said, a bigger pre-scaler on the PWM module would be nice,
because.....

.....I've got a project part-done that requires, amongst other things,
pot-controlled frequency and PWM of two (at this stage) independent
channels from 0.1Hz to 300Hz. Processing time needed for this is
starting to impinge on other functions and I'm thinking of bit-banging
the frequency/duty cycle from the PIC over to a couple of Scenix's or
satellite PICs, let them do all the donkey work in s/w

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