No check engine lights or computer code indicates a problem, yet when the truck is brought out on the highway the RPM gauge oscillates quickly and the Xterra SE loses power, will stall out, and then will be difficult to start up again until you wait a few minutes. My usual mechanic had the truck for 2 weeks but could not recreate the problem in his garage and would not take it out on the highway because he did not want to get stuck. I picked up the truck last night and it broke down again on the highway with the same symptoms. I had it dropped at the Nissan Service center last night as my mechanic could not figure out the problem. Any ideas?