I'm not sure it sounds behavioral. It sounds like he's still doing the suck-swallow thing and he hasn't really learned to chew. Perhaps an SLP (speech-language pathologist) who specializes in feeding therapy can help. This would be instead of, or in addition to, an OT who does feeding therapy. They have totally different approaches, as the SLP has very detailed knowledge of how the mouth works.
My DS was doing something similar, and he has SPD with HUGE mouth and hands texture issues. First, just a look at the food texture was threatening to him. Then, he didn't know how to chew, and I think he knew that. Whenever he got something he had to chew in his mouth, if the texture didn't gag him, it scared him that he wasn't able to coordinate the chewing motion, so the food always came back out. Add to that his general anxiety issues, and you have one kid totally afraid of food.
The SLP identified his oral coordination issues and worked with him first on learning to chew on non-food therapy items. She also worked on texture desensitization both inside and outside his mouth. Then she worked toward chewable food items. After that, she worked with him on play-based feeding therapy to help him get over the fear and texture issues. All of that was very helpful. However, we had to get and pay for this privately, though our insurance covered a portion of it. I had to call around and ask a lot of questions to find the right therapist. EI (early intervention) where we are located and other feeding therapy places just weren't equipped to handle it, as we wasted about a year without results from those places.
mama to DS
12/2005, Pepper kitty