Cruise control problem

My 89 Silverado is experiencing problems with the factory cruise control. The cruise will no longer maintain the set speed - speed slowly drops off after setting the cruise. The accelerate function does not work any more. It
feels like the servo is still partially working as when you touch the brake or turn the cruise off, the truck decelerates noticably as it normally would when the cruise is deactivated.
I did a little looking on the auto parts sites on the internet but didn't see anything like the servo unit I have in my truck. Frankly, I don't know if it is the servo unit anyway...
Any and all help appreciated,
Thanks in advance,
Gurbax
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Replace the diaphragm mounted to the back of the block or the vacuum lines that run it.

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I crawled around the engine compartment and couldn't locate anything that looked like a diaphragm or any vacuum lines at the back of the block. About all I can make out is a cable connected to the TB linkage that ties into a 'control box' on the left (drivers) side firewall. There aren't any vacuum lines running to this control box either. There is only one multiwire electrical connection that attaches to this box. Its nothing like the pictures of the diaphragm unit that Ive seen...?
Im stumped. "Shades" <shades_1970(at)netins(dot)net> wrote in message

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