The new MUT Levels are out now and it's worth noting that EA has tried to make it much harder to do these kinds of MUT Level grinding techniques. We still have a way even though it isn't as efficient as before.
Check it out below.
Go to Madden Ultimate Team
Click on Challenges
Then click on Rivals
Next go to Quarterfinals: Challengerz
Pick the Quarterfinals: Challengerz V
Set the difficulty to easy
Put your fastest receiver on a streak throw it to him and run out of bounds at the 40
Overview: This we have found to be the most efficient way to grind the new MUT levels (50-60) that recently came out. Even though this has been found to be the most efficient way it is still a very long process so don't expect quick results.