cruise control problem

have a 2003 Xterra and when using the cruise control for anything above,
around, 75mph, the car learches quiet badly. It's as though the cruise
control is having a hard time maintaining constant speed at or above the
75mph limit. Below that, cruise control is very smooth. The dealer said,
after test driving, "this is normal." I simply don't buy that. I've never
driven a car with such sloopy controal. Anyone have any ideas regarding
this. Is it typical of Xterras and/or Nissans? Or is this an atypical
problem the dealer really should fix?

Thanks,

jim

I've never had that problem occur - do you have an auto? It could be that the transmission is shifting up and down constantly (or maybe the torque converter is locking/unlocking) to maintain speed. I have a stick, so I'm not sure how much an auto would struggle.

Yes, it's auto, but as near as i can tell, it's not shifting at all.