The transmission is a type 4T65-E and the owner's manual calls for use of GM Dextron III automatic transmission fluid.
After replacing a leaking pan gasket I need to fill the transmission case with ATF fluid and my question is: "Is there any reason why I should not use an aftermarket product e.g. Valvoline, Mobile, Chevron, etc. ATF fluid that is marked as meeting Dextron III specs? This fluid is much cheaper than the GM Dextron III fluid sold by the dealer and it's supposed to meet all of GM's Dextron III specs.
Ray