Cruise control problems

[winnipegk5]

I have a 79 Suburban that I am trying to get the cruise working on. It is a 2wd 350 AT. So far I have:
1) Power from the switch to the controller it clicks on and off when I push the end of the turn signal
2)The speedo works fine and is accurate
3) If I provide vacum to the throttle actuator it pulls the throttle linkage.

Nothing happens when I put the cruise on at highway speed. I can here it clicking under the hold but it will not maintain the speed.
Any tips would be much appreciated.

Thanks in Advance
Mike