If you are sure it an accurate test, this is not normal for this lens.
I have run the same test on several copies.
Most copies would be at the best around F/4 with almost no drop of at f/2.8.
Some copies would be sharpest at f/2.8.
The curve should remain almost level after f/4
I am sure it's accurate. It's how I have tested all my other lenses and I have never seen this.
Thanks for the input.
First to call the store I bought it from to chew them out for not giving me another copy and making me go through this, and then a call to Canon to see if I can get this replaced.