I just went through a hesitation, power loss problem on steep hills with my 2000 Lesabre with about 90K miles. The dealer looked for codes and the knock sensor was bad and the catalytic converter. The dealer replaced the knocksensor, and a local muffler shop replaced the catalytic converter. I drove the car, and it was better, but it would still hesitate and cut out at times on steep uphill grades at 70 mph. Then the car got much worse a week later, but only on steep unhills at highway speeds. On flat ground it was fine. I took the car back to the dealer and a now the mass flow sensor showed up on the codes. They replaced it and it completely fixed the problem.The dealer did try cleaning the mass flow sensor. It helped, but didn't solve the problem. Hope this helps.

 

That part is actually known as the mass flow sensor and can be picked up @ any auto parts store. I haven't replaced one myself but, it's on top of the throttle body most times or on the side and should not be that big of a job. I priced one online for my 89 from advance and there asking just under 200 bux for it so, it's a little bit to buy but, it's better than a car payment.[img]smileys/smiley2.gif[/img]