It's not quite the same, but spend some long sessions on Forza. If you can, do it on the track you'll be driving next so you can get some of the layout ingrained before you show up. Drive yourself around the track in your head. Like others have said, you're likely dealing with mental fatigue and these things will help make visual markers more automatic so you're concentrating less on when to brake, apply throttle, etc.
And a few tricks to get your brain prepped I learned Mr. Bentley when he was in Denver a couple of years back: cross-crawls and thumb figure 8's while sitting on grid... tongue on the roof of the mouth and reminding myself "eyes up!" while driving. Thanks Ross!
