Problems with a 2000 Xterra

I have had the xterra for 2 years. The air conditioner has never been quite right sometimes works sometimes doesn't. Since I live in the tundra I only needed it a couple of months a year anyway. The speedometer odometer and cruise all stopped. The big issue is losing power while driving. The mechanic thought it was the fuel pump but decided against it because once you stop it and turn it off and start it up again it will drive for hundreds of miles without any problems. However it is still happening. Any ideas?