2002 Chevrolet Suburban Transmission Fluid change over 200,000 miles?

[Superwoman22]

I have a 2002 Chevy Suburban 1500 2 wheel drive. The truck has over 200,000 miles. I was told by one mechanic that I needed to flush the fluid only and not to open up the transmission because of the high mileage. I was told by another mechanic that changing the fluid and filter would be fine and would not present a problem regardless of the mileage. If you are familiar with this, what is your take on this? If I don't need to open up the transmision, I can drain the fluid myself and put new in, so I want to get a heads up about it so I know what direction to go in. Thanks in advance!