GVW stands for Gross Vehicle Weight (total weight of vehicle including trailers or towed vehicles). I hope that helps, that's off of the B&M website, so i guess you match your vehicle weight with the rating on the cooler. I guess.
Just keep in mind, if you can lower your trans temp 20deg, some say you double the life of your trans. For me, everytime i don't go to the track, i extend the life of my trans one more week, lol.

i'm sure 24,000 will be just fine. It's easy to install, and should take you a couple of hours, when ppl ask how to put it in, i say in series with the stock radiator cooler, but if you get that B&M cooler, you can just plug off the radiator and use the cooler, i guess whatever is easier.

good luck,

allen