99 Taurus

I have a 99 Taurus which I bought with a three year extended warranty. Nine (9) times the dealer has worked on or "looked at" the transmission. The tranny slips going into second gear within the first

15 minutes or so of driving, and seems to rev very high in neutral -- over 5000 rpms at times! It also nearly got me killed when I tried to pass a car and the tranny again went into what seemed like neurtal and there I was caught in the passing lane. They have replace the speed sensor, flushed the tranny and tell me there is no metal, and did another repair. When the dealer billed me $400 the week of the flush just after the warranty ran I out I balked. The car still slips when relatively cold and again failed to kick into passing gear on a recent trip. What if anything will fix this tranny? The dealership has had it a week to "check it out" and wants if for another. They claim they cannot duplicate my problem and that there is nothing wrong. Am I crazy? Or, is it possible I am being misled? I certainly can't afford to replace the transmission, an option the dealer suggested two weeks after my warranty ran out!