automatic cruise control, unwanted

[00 6.0 4x5sp]

2000 6.0L, 5 spd, 4x4, ex-cab, swb.  Notice: 5 speed, manual.  

Get this truck over (about) 1700 rpm's & it'll maintain speed (foot off the gas) till it hits a big enough hill.  It'll gain speed/acceleration down the hills.  It's kinda like the cruise control is on.  

The big problem is when out of gear & rolling, motor will rev way up, eventually bump itself down, then wind-up again.  BIG PROBLEM-  Can't just take it out of gear & coast down, unless you wanna hear that motor wind out.  

Usually a buzz sound, similar to a street light buzzing happens around the same time, not sure if related.  

Already replaced a throttle control.  Have been told wiring problems are common for 2000?  

Any ideas ?  

Thanks.  

[Formulabruce]

 Clean the Throttle area, including the throttle plate, and use throttle cleaner. Get it perfect. should fix this problem. Make sure air boot is tight .

[Supreme Pizza]

Ya, I would agree. Clean the throttle plate. Carbon may be holding it open. Remove the intake boot, and have someone push down and let up on the throttle several times, while you watch the throttle plate. Definitely check for air or vacuum leaks too.