Gig speed internet

Alright orignally I was on the Blast! speed tier with Xfinity getting 300mbps download speeds. I was having issues getting those speeds but on good day I was seeing anywhere from 100-250 mbps download speeds over wifi. I have about 30 connected devices on my gateway at any given time. I just recently upgraded to the Gig speed internet plan today and I am now only seeing around 100-150 mbps download speeds over wifi. Is there something wrong? Am I missing something? When I hardwire my laptop to my gateway I am seeing about 900mbps easily but for some reason I am getting worse wifi speeds now with the Gig speed plan then I was getting with the Blast! 300mbps plan.

Any suggestions?! 

Thank you!