I highly recommend the coolant flush because I had a BAD experience using long life Prestone in a '97 BMW 328. Since then, I use BMW antifreeze that I buy on line, as it is prohibitively expensive from the dealer.
Fresh oil in your automatic tranny every 50k miles will make it work better and last longer, but a common cause of quirky transmission problems is a failing battery. The computer that controls your transmission likes a strong battery and nice clean battery terminals. If it does not have them, it can do some weird stuff.
If your radiator external reservoir is original, it is likely crumbling inside by now. I could never get all the air out of the cooling systems on my two '97s until I replaced those reservoirs. I cut one open to see what was going on and the tube that runs down inside the tank had a big hole in the back.