PCV valve, mmmmm possibly, unlikely, it would show up at idle speeds more than cruising speed as would a gunky throttle body.
I checked out a couple of sources for similar complaints with his Isuzu, the most common for driveability issue(not a surging issue though) has been a corroded Engine Coolant Temperature sensor wire, the fun part is the sensor and subsequent wiring are under the intake plenum. I can remember doing one a number of years ago, I remember thinking the engineers were out to lunch the day they decided to put this sensor under the plenum. I did see a few complaints of surging, hesitations, etc., unfortunately no fixes were posted, but I have seen some unhappy owners having to rebuild their transmissons at 80,000 - 100,000 miles, which in my books isn't that bad anyway, well 80,000 is a little short but 100K(although most do go well beyond now adays) is what most cars are designed to live to, anything beyond that should be looked upon as gravy. Of course if most of the driving is highway the the mileage will be increased substanially before breakdown.
