EXP experience gain

Hello, I am now lvl 65, on nightmare difficulty, just started 10-1 stage. 

I got 3 stars, and total exp of 1000. Why is this? 

when i was a few levels lower, on stage 9-1 and 9-2 I got 3000+ exp for 3 stars. how should we level up while receiving lest than 1000 exp per level, which is 1-2% of our level? 

Nightmare 10-10 cleared 3 stars, 3724 exp, what is going on?

[IMG]http://i66.tinypic.com/2lihu3b.png[/IMG]

[IMG]http://i68.tinypic.com/214vcli.png[/IMG]