1996 Chevy Blazer Accelaration Without Pressing Gas Pedal

I have a 1996 Chevrolet BLazer LT 4x4. Recently, within the last month I've noticed when driving the car will accelarate slightly a couple of RPM's on it's on, even when the gas pedal is not being pressed. Sometimes at high speeds (~70 miles/hours) it will do the same thing, but typically only if the cruise control is on. It's very subtle but you can definately feel the car jerking forward. I also notice that sometimes when the car is placed in reverse the 4 wheel drive will turn on by it's self; when I press the gas pedal the engine rerves but nothing happens unless I give it extra gas. Not sure if this is related but the fuel pump was replaced almost 3 months ago. Thank you for your response.