Took my 2008 nissan sentra to the hoover dam and after about 2 hours of driving, the speedometer drop with a whining noise and the RPMs going to 6000.

I suspect a bad ground...clean the other side of the 1/0 cable that comes from the negative terminal....goes to the fender/frame...coarse wirebrush this connection, the place where it attaches and the lug itself...this high amperage connection "welds" itself with each use and is shared by the onboard computer and ignition system~ thermal expansion and contraction have played hell with this critical ground connection causing a "brown power" failure...pulling a battery cable waiting for 15 seconds and back again should clear the CEL~

the throttle position sensor can go kafluey after X-hours of use_____ http://www.ecrater.com/p/16457293/throttle-position-sensor-tps-fits? gps=1&id=52211034499

Copy that. I checked the ground on the negative cable attached to the fender well, and it appear ok with no corrosion. However, how do I check the throttle sensor? Will this make the car feel as if the transmission may be slipping? Also, all fluids were checked and ok. Thanks

I have the same problem. My car would make a whining sound if I drive a steep uphill or drive straight longer than an hour. At first (for 2 years) it was just a sound and then I recently noticed that my RPMs would be shooting up but my speed wasn't going anywhere. I read that because nissans have CVT transmissions, there isn't enough time for the fluids to cool off after it passed through the transmission cooler. I read rare few cases where people installed an additional* transmission oil cooler to their car and it corrected the problem. I just installed one today but I have not tested it on an hour car ride just yet to let you know if it worked for me. My car makes the noise but when I let it rest, it worked fine again because the fluids were able to cool off. Similar to your situation.