I am going to be replacing the flex plate in my 2003 gmc envoy and my question is, do I have to completely drain the transmission and drop it completely? I was thinking I could just unhook all lines and linkages unbolt the drive shafts and transmission and just slide it back far enough to be able to replace flex plate. Is this possible and if so how much transmission fluid would I lose if any? I didn't even think to check the flex plate when I changed transmissions and torque converters. Any help or advice/tips is greatly appreciated!!