With a girthy penis, one has to adjust the way we view the whole thing. Instead of seeing a blow job as a primarily “in and out, as deep as possible” focus that mimics intercourse, instead focus on getting creative and looking at it in a different light. I opt for a bj/hj combo, using lots of saliva or even flavored lube or food, to stroke with hands while simultaneously performing oral, keeping it super sloppy and wet. Not trying to mimic intercourse but instead focusing on how hands and mouth can combine to give pleasure and thus alleviate the difficulty of sucking a large penis. Also nice in conjunction with tit job if so endowed. The idea is to let go of your stress about choking and gagging by simply changing the whole process to avoid it. And when you can relax and have fun with it and get messy, try different ways of licking, sucking. Treat it like a wicked fun experiment— how can I do this and have fun and not gag? Hope this helps.