C.H.
Hi K.
I'm not trying to jump the gun here, but he sounds like he is orally defensive. Does he resist brushing his teeth? You said he doesn't even mouth his toys. I would talk to your doctor about it and maybe see an Occupational therapist. With the gagging, I would think it is more a texture issue than an actual food issue. OT's can really help desensitize and set you up on a program to help you both get through this a little easier.
Good Luck,
C.