All caching plugins should work with GeneratePress. WP Rocket is a popular one.
If your site is loading slowly, the first thing you should look at is your hosting. I find that hosting is the #1 cause of a fast site, and good hosts will have built-in caching so you don’t even need a plugin.
Thanks, Tom. I am with Siteground until August. They have caching with something called SG Optimizer and I have that activated. Should I switch hosts? I will try WP Rocket meanwhile.