This problem first happened in Oct 2011 when the weather started getting cold, I would be driving down the highway, and the RPMs would rev up slightly although my speed never changed, this became more and more constant as the weather grew colder. My uncle who is a mechanic suggested that it might be the transmission speed sensor. A few weeks later, my check engine light came on, which freaked me out, so I had the check engine light checked it read back speed sensor. So I bought a new one. When I replaced the old speed sensor, I noticed that there was metal shavings on the tip of the speed sensor, which according to my uncle, kept the speed sensor from properly reading the speed, and letting the transmission shift properly. After replacing the speed sensor, the rev-ing problem went away, until just recently when the rev-ing issues started back up again, in August 2012. Quick fix is to remove the speed sensor and wipe off the shavings causing the reading issues. Long term fix repair the transmission. :(