I have this same problem on a 2001 Bazer. Bought it used with just 38k. Didn't notice this until taking a long hwy drive.
It is almost an imperceptable hesitation, and only noticable at highway speeds, but very annoying and worrisome. I first discovered that it only happens when the airconditioning is on, but then discovered it happens when front defroster is blowing as well. Doesn't seem to happen when just the blower/vent was running. I haven't checked yet on heater. It happens with cruise control on or off.
It does not happen when the air/defrost etc is off. Anybody have any idea what this is?