raychevy,
The guy is trying to rip you off. I can get a flush for $50.00. A complete tranny oil change for $69.00. A flush is good if the shop knows how to work their machine. I've had it done to one of my trucks. Pretty simple. If you are really worried about your oil put a drain plug on the tranny pan when you change the filter. Remove a quart at a time every month until the oil looks clean. Keep the oil topped off and you'll be okay.
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Gerardo
1983 Custom Truck
TX Plates: "BAD BOW"
http://www.geocities.com/abetterchemist/