2006 maxima goes from (D) drive to 5th gear???

[ajnissanmax06]

I have a 2006 maxima. When i turn on my car and drive about 1/8 of a mile it goes from (D) drive to 5th gear on manual mode. After that everytime i stop i have to give it more gas to go because it stays on 5th gear til' i park and turn off car. that happen about 4 day ago. ffirts time that happen "check engine soon" light turn on. Anyone has an idea why this happen, i need help. tnx

[ajnissanmax06]

I got a second opinon from a transmission shop and in their scanner it wrin up code P0726. They told me no reading is coming back from the (turbine speed sensor). In case of any of those two things being true, is there a possible way that i can do this repair my self? If yes! Where and how much am I looking to spend in parts. In what part of my car will I find this sensors? I appreciate your believe MinisterofDOOM

Tnx folks for any answers?suggestions to my trouble.....