98 grand voyager cruise control problem

Just recently my cruise control decided to stop working on me. It'll hold on the highway for about 5 minutes and all of a sudden just let go. It may hold on again for another 5 minutes, but after awhile it'll just not work whatsoever. if i try it the next day it may be fine for a half hour, but it'll always eventually let go. Any ideas where I can start my diagnosing? is this thing vacuum operated? is it a heat issue after the engine warms up?

My cruise control did exactly the same thing. The problem was a vacuum leak. On my '96 3.8 van, there is a vacuum line that runs from the plenum to a vacuum reservoir under the battery shelf. That line was hard plastic that had gotten brittle and cracked. The other line that comes out of the vacuum reservoir goes to the mechanism that pulls the throttle cable for the cruise control.

Thank you very much, i'm gonna check that this weekend.