I have a 2012 3500 crew cab long box with a afe dry flow intake, sinister egr delete , smarty senior, 5inch turbo back

Before winter I was getting 19 to 20 on the highway doing 80 now I'm getting 13.9. Don't know why it dropped so fast in one day of driving?
Any ideas would be much appreciated talked to a few diesel guys and they couldn't point me any any direction,
New air filter fuel filter oil synthetic