Problem with 24-70 canon lens L iiUSM f/2.8

[indigo343]

HI, i recently bought a new 24-70 L ii USM f/2.8, i used to have the same one but got stolen, thats why i replaced it. The problem is that it feels like this one doesnt have as much light as the other one. I have to put the ISO quite high even in 2.8 aperture to get the shot, and the grain is quite bad. That didnt happen to me with the prior one i had. I need some advice about this, is there something Im not doing? I really appreciate the help, since it was a very expensive lens I choose to buy....again. Thank you very much!