I have one more thing to throw in here. Let's say you have an intermittent problem on your vehicle,say a .........'02 Dodge Caravan and it doesn't want to upshift sometimes. You might have to drive it a whole day to get it to do it. Would you rather a shop put one sensor or part on ($50 -$200)and then let you drive it to see if it fixed it and then bring it back again if it still does it,or would you rather they replace everything possible (maybe up to $500-$600)that would cause the problem and the problem be fixed?
Thanks everyone for their replies. 
I'll just chip in another
on this. My wife's family (and with great pleasure now myself) has been Mopar for life, so we have gone through 5 or 6 Chrysler minivans, ranging from 94 up to our current 2005. If you are having ANY kind of tranny problem, I feel that you need to go the whole 9 yards on getting it rebuilt. Unfortunately, the late 90's early 00's Chrysler minivans are notorious for losing transmissions. We had to rebuild a couple of our earlier ones. Our previous van started with similar symptoms (would not shift to 3rd), so I replaced a solenoid for around $200, but then less than 3 months later had to do a full rebuild (another $1,500). At a minimum I would for sure take it to a Chrysler dealership to get it checked out, as opposed to the local tranny shop. It might cost more for a diagnostics, but I would feel better that way.
