Randomly got a bit of extra GG XP today, which got me the Season 3 XP boost. Then I just had to complete the daily objectives and got to level 51!
And Gronk is insane. Loaded into H2H, literally first play he pancaked a linebacker. He's a great pass catcher too. Picked up 26 yards on his first ever catch fully upgraded.
I'm running Vanguard and SIE on him right now.