I have had this issue off and on for years. It will be fine for months at a time, then it just go into this mode out of the blue. It starts hard, and then it's stuck in 5th gear so acceleration isn't there like in 1st gear. Most of the time it will reset by itself if I turn it off, wait a minute, then start it again, but not always. And if it does reset to normal, it could go into this mode again later the same day. Happens in all weather conditions, so that's not it. The code kicks out a camshaft position sensor circuit malfunction, and I've had it replaced three times by the same mechanic in a year, the second and third times at his own cost since the part was under warranty. It's been a good 10 months since it happened last, but here we go again! I wish I knew if there's a way to prevent this from happening again. Also, as a side note, I have a problem with third gear. After the engine warms up for 5-10 minutes driving, 3rd gear will not go into 4th smoothly but and it will jolt me. It's much worse when I'm driving up hill. Anyone have any ideas on these two transmission issues I'm having with my 2005 Altima SER 3.5? Thanks