I have a 97 Dodge Ram 1500 4x4. When I drive it for 20 minute or more this is what it does:?

When I let off the gas the RPMs go down as normal but then they will shoot back up. Sometimes it will hang until I tap the gas. No warning lights come on. I have done the OBD II by turning the key and no codes come up. It does not do this if I drive it for shorter periods of time. When it does this it does not accelerate. I have had the throttle body clean because at one point it was stalling out at traffic lights. That problem had gotten worse to where it was stalling out every time I let off the gas. Does anyone out there have a possible solution to this problem?