I was driving my 2001 Pathfinder SE (manual transmission) last night, shifted from 2nd gear into 3rd and felt some vibration, like driving over coarse gravel (the roads were a mixture of packed snow and dry pavement). It kind of felt like I had shifted into 5th gear by accident - but I hadn't... It got worse as I accelerated... I shifted back to 2nd and the vibration increased as RPMs increased. Then I shifted back to 3rd and vibration started again, and then the check engine light came on flashing, went off after 10-20 seconds. I pulled into my driveway, turned off and restarted and it seemed to run fine. Has anyone else encountered this problem? Any ideas what it could be?