For this reason, the "grades" in the first two years of med school don't really matter all that much. It's the "dirty little secret" nobody tells you, but residencies are going to focus on your Step 1 score and clinical rotation evaluations as your "grade". Nobody cares if you had a 3.5 or a 3.0 or even a 2.8 equivalent in the pre-clinical years. If you passed everything and learned enough to do well on Step 1, you are in good shape. It's a pretty different world than undergrad, where course grades actually impact your GPA and thus are meaningful in terms of your next station in life. Getting a pass in a pass fail med school course won't impact your life.
It also ends up being humbling in med school because most people who get into med school are high GPA types who can't imagine being in the bottom half of the class. Yet half will be in med school. The admissions folks do a great job of truncating out the folks from college who made most of us look good during our undergrad years. Now the worst person in med school was someone who still got their share of high grades in undergrad, and so the competition to even just be average is now pretty intense. Which is why a lot of med schools do the pass/fail thing -- to try and serve as a safety valve for intense competition, basically acknowledging that the only "grade" that matters is on Step 1.
Step 1 is a beast, and the best way to pre-prepare for that test is to work hard in the first two years of med school. No way you can learn it all the summer before the test. If you are doing well in med school, you spend an intense 6 weeks "refreshing" and can do fine. If you are struggling in med school, there's probably a good correlation with being less ready for Step 1.