Lincoln/Mercury Repair: 99 Cougar Check Engine Light, o2 sensors, cougar v6

Question
I've had an ongoing problem with the sensors for a while now.  The dealership replaced the MAP sensor under warranty but the light came back on after the warranty expired and I had it replaced again.  It didn't take too long before it came back on.  I just drove it like that but last year it failed inspection and the local shop said it was the DPFE and o2 sensors.  The light stayed on but replacing the DPFe was enough to get it to pass.  Now a year later, the car is running poorly and I want it fixed once and for all as long as its reasonable.  I was thinking of having them replace all of the o2 sensors in addition to some other tune up work they are doing.  What do you think I should do?  I would just like to be educated when I speak with them.  

It is a 99 cougar v6 manual with 144,000 miles.

Answer
hello '
it seems to me some one is misleading you once they do a diagnostiac test on your car and tell you the problem it should fix the problem.
you tell them you want it fixed for the money you have already spent .
a good tune up will not hurt it is good
pete