1996 C1500 4.3 Stick Shift Idle hunting in nutrual.
 

I have this really nice Louisiana 96 C1500 4.3 Stick. I like to pop it into nutrual when coming up to a light or going down a hill. When I do this my expectation is that the engine will go to idle so I can save a little gas, and some times it does go to idle (750-800 rpm) and then sometimes it hangs around 1500 rpm. a couple times while it was hanging at 1500 in nutrual I kicked the gas pedal real quick and it shot up to 2000 rpm and hung there for 3-5 seconds then down to 1200 and eventually to about 1000 rpm but rarely goes to 750-800 but it has gone that low on occation. I took it to the Chevy dealer and of course it wouldn't do it for him while he had the code reader hooked up to it ultimately he got nothing to show a failure. has anyone had this happen and if so were you able to fix it?