4 month old gets burps trapped

My 4 month old has been on enfamil gentlease for months, but he always seems to get his gas trapped. Sometimes he burps fine but a lot of the time especially in the evenings he ends up choking on his burps almost like hiccups and it takes several gas drops and about 20-30 minutes of wailing before he gets relief. 
He can be an aggressive eater but he can also take him time and not finish a bottle. We use tommee tippee bottles and he's still on #1 nipples. 
I thought about switching to similac sensitive. Any recommendations? Is this just normal baby gas issues?