I have a 2007 Maxima. Recently I have been having issues with what I thought was the CVT transmission. When the motor is cold it runs fine. Once it is up to temp the rpm will jump, but the speed will slowly decline. I have changed the Transmission Speed sensor and the Mass Airflow sensor. My speedometer is approx. 5-7 mph higher than the actual speed so I thought it may have something to do with that, but I am unsure. Has anyone ever had this issue? Any help is appreciated. The car goes into a sort of limp mode once the motor has reached temp.

 

I recently had a similar issue. I would accelerate to 40-50, then when I'd brake, my ABS would go off and I wouldn't be able to accelerate whatsoever. Turned out to be a bad Wheel Speed Sensor (right rear). Apparently, it's a common issue, and a bulletin was sent out by Nissan once the problem surfaced, but none of the previous owners or shops saw it, or they didn't do anything about it. Maybe have a shop run a diagnostic test on the Wheel speed sensors and ABS sensors? I replaced all of mine after finding out that that is what the issue was and now she runs beautifully.