Where are you getting that rating? I plugged the ESPN Numbers (6/23, 214 yards, 3 TD's, 1 INT) into two different calculators and both times came up with 87.32. Calculator 1 and Calculator 2.
Now if you are serious about comparing him to Peyton Manning, his numbers are 3/17, 79 yards, 3 TD, 2 INT, for a rating of 46.45.
If you're talking about last year, then yeah, his numbers weren't great, but if you measure greatness by the "number of long-ball attempts" he threw more passes over 20 yards than Manning last year as well as this year (82 to 64)....