Daryl:
I'm assuming this is a single engine aircraft. If so, this prop is oil to high pitch (low RPM). If I understand your problem, you are able to go to low RPM, but the return to high RPM is sluggish.
For your prop to return to high RPM, your governor simply "dumps" the oil out of the prop. This is an actual mechanical action - your action on the prop control is physically lifting the valve spool in the governor to dump the oil.
I'd venture to guess that your governor will check out OK, and that the problem lies with your prop. It's probably cheaper to get the governor checked first - as mentioned, it is simply a bench test, whereas your prop will most likely have to be diassembled to determine if the problem lies with the prop. My best guess is you either have a "sludge" problem, a problem with the blade bearings (corrosion), or the hub is full of grease. On a Hartzell prop, if the grease procedure is not carried out in accordance with the manual, the hub can fill with grease and the prop will either be sluggish or not cycle at all.