'86, 305, auto, 87K miles.
It seems to have always done this, in talking to the previous owner. If I want to set the cruise at, say, 50MPH, I have to run it to 55mph, set the cruise, then let off the gas. When it coasts down to about 50, it'll grab then stay at that speed. Although, sometimes it doesn't grab, so I have to speed back up and set it again until it does.

When it works, it works great, but I don't like well-exceeding the speed limit just to set my cruise control...

 

Take some of the slack out of the cable. When you get it right you will hardly notice when the cruise control engages and it will hold a steady speed. That's provided all other things are working correctly, such as vacuum, speedo cable, etc.

 

Thanks, I'll check that out