It happened the other night briefly, but has also since then occured three other times within the last 2-3 days....in between shifts, there is an extreme hang in rpm or even a rise in rpm, then it idles at 1250-1400rpm. After a few minutes of driving and maybe some WOT, it will go back to normal....wtf? If it were a vacuum leak, it would probably be more consistent I would assume. No CEL, nothing...input? 56k miles.
