cruise control troubleshooting

vehicle is a 1998 Chevy K-1500 truck problem is cruise control is very erratic when you tap the switch to engage it, it can take anywhere from 30 seconds to 3 or 4 minutes before it engages, and when it does engage, it
won't hold speed very long, especially on hills. Did a visual check to see if there was a loose cable or electrical, but everything looks ok. It'n not a vacuum system, so no loose or cracked hoses to worry about, right? Any ideas on what to look for before I have to take it to a dealer and pay $300 or more for them to tell me it's a broken widget?
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You could probably find a good one at a junk yard for less.
Cheers
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