There is an aftermarket cruise control that requires no vacuum source
at all. Uses an all-electric servo to operate the throttle. I got one
and installed in my suburban 6.2 Diesel to replace a bad stock cruise
(which relied on vacuum from a pump).

Works just fine, but quit the other day when the speedo cable died (no
surprise there, eh).

Comes with a speed encoder that inserts in the speedo cable, but I
think it can be configured to read speed pulses from an existing
sender on the vehicle, if one exists.

Let me check in ths hop tomorrow, and I should be able to find the
maker's name.

Gord Richmond

I have cruise control on my supercharged Avanti. I used the Audiofox
unit with the magnets on the driveshaft. Works very well. I put a
vacuum canister from an old Chev. Celebrity in the vacuum line so that
under boost conditions the cruise does not lose its setting.

KOOL R2