here is the fix thanks to Mike Dolan
I don't know if anyone has the same problem I've been having when appling cruise control. When I hit the set button the truck would sound like it was floored then settle down, but the cruise control was not steady once set.
I had read about installing some kind of adjustable valve inline with control module, but I could never find one.
My solution was to put a spray tube (little red tube) from a aerosol can inside the vacuum tube going to the cruise control module under the drive side battery. The tube fit perfectly inside the vacuum line, I left it a little long so if I ever wanted to remove it I could still take it out. The small inside diameter of the spray tube seems to be just right. Cruise control works great now.
I installed the tube up by the T connection on the firewall.
I thought I would pass this along in case anyone else was having the same problem.