I don't know if you have managed to get your grills off yet.
I had real trouble getting mine off - one side eventually, with a lot of tugging. The other side would not budge until I used a trim removal tool (bit like a screwdriver with the end bent up a bit) working my way along and freeing each 'tab' in turn by levering it out of the retaining hole. I also gently warmed the plastic with a hair dryer to give more flexibility.
I put a smear of silicone grease on each tab and hole to make life easier to replace and take off in future.
Best of luck buddy!