I've never noticed this and I do a considerable amount of highway driving. Maybe it is something like the DIC warning you when you're running low on fuel. Perhaps it is a difference in our driving styles but, just in case, I'd ask at my local service department. I would not be messing with a potentially sticking gas pedal or would I use a wedge to "improve" response. You may believe you know what to do when a throttle sticks at a high rate of speed or in a panic situation but not everyone driving your truck may be as prepared.