accelaration issue

I have a 2003 Bonneville,3.8) which, my son uses at college.

Great car over all but lately it will gradually increase its acceleration on its own.   This may occur while it is at idle or while being driven.  It will usually slowly increase in RPMs from .08 up to 1.5 or even up to 3K RPMs at times.  This is usually more of an annoyance, but fear it may become a safety issue when it remains around the 3k RPMs.
I have replace MAF sensor, idle Control valve and the throttle control sensor but it still continues.
It ran great for a few days after replacing the idle control valve, but sure enough, after a few days the symptom appeared again.
The acceleration may occur when the car is cold, or when it is at running temperature.   

They only other symptom it has is that it will miss while shifting or appear to slip in and out gear, when this is occurring.  When it is running fine, it shifts quite smooth, but when the acceleration issue occurs, it will generally jerk while shifting gears as you accelerate.
The only other thing I could think of is a vacuum leak but have been unsuccessful in finding one in a hose or around intake.

Thanks for any help!!