Problem with 4WD Nissan Navara

It happens that I have a 2010 Nissan Navara and I was starting to cause problems with double.
1. The double light was turned on and it was slow,
2. The velocimetro walking up and went down and began to flash but the tacometer if it worked normal and the car every time it accelerated the velocimeter worked normal but there were times that lowered the acceleration that can be.