variable high rpm when shiting gears

I just bought a 94 ranger 4x4 extended cab with the 3.0. I drove it to work the other day and after it was warmed up a bit, when shifting gears, the rpm shot up to 4500. This happens only when upshifting, taking my foot off the gas and pusing in the clutch. If i simply hit the gas when in nuetral, it tends to stay at a higher rpm and then very slowly go back to idle. It has hit 4500 only about 4 times, but every time i shift up, the rpm stay high for a brief period before dropping. I have checked the IAC valve, and also for a sticky trottle. Any ideas? I am thinking either electrical or something in the trottlebody. Thanks in advance.

I went through the same thing last year on my 3.0 95. I was told to check for vacuum leaks. I finnally found a cracked hose going to the carbon canister, front drivers side under battery. check all hoses by spraying carb cleaner on them, while truck is idling & listen for change in idle. Carb cleaner didn't make difference on this hose though, I found it by feel. Good Luck!