Recently I have noticed while after driving the car for a good period of time on the highway, I've felt that I've been getting a "pulsing" out of my car while steady-state cruising at highway speeds. It seems to happen while around 1500rpms-2000ish rpm with steady, or very light throttle inputs. I replaced the distributor a while back for a seemingly unrelated problem, so I don't think that's it (ya never know though) and I have no CEL on. The problem only seems to happen after the car has been driven for a while (45 minutes or longer) and it never feels like it's going to stall, but there's a definite pulse/miss/bog to the way it feels, and you can see the tach respond to the motions too so it's not just road bumps or anything. Any ideas of where to start?