Crank shaft censor?

1999 Oldsmobile Intrigue, 3.5,104,098miles. When I drive my car does not pick up speed. I took it to auto-zone and had a free diagnostics scan done on it and it read that my crank shaft sensor was bad. The part is about $60. A mechanic I talked to about it said that the scanners that auto zone uses are not reliable. He told me that if I brought the car to his shop he would charge me $65 for a diagnosic scan and that the crank shaft sensor was more than likely not my problem. The car still runs, but as I said when I am trying to speed up it delays getting up to speed at times. Should I pay for another diagnostics test or just replace my crankshaft sensor. I also noticed a burning smell coming from my engine that I usually smelled when I got on the Hwy. But it was not strong and lingering. Usualy my car would pull, like it was trying to switch gears to get up to speed.