Ok - first of all I have no idea what you mean when yousay stage 2 +3 foods :? , but if gagging and vomiting is the prob......
Try sloppy food that have more lumps in them firstly and once he can manage and understand how to swallow lumps
Try solid foods that turn mushy in the mouth, eg toast fingers, rusks, banana, cheese, avocado, peaches are just some that I can think of now
See how you go with that, and don't be put off by some gagging or even vomiting at times - all part of the learning curve - he'll get it in the end
Good luck