Son Suddenly Struggling With Math

my son is 17 and has always done extremely well in school. this is not me bragging. I truly have very little to do with it. he's just always been a kid who loves to learn and a very ambitious person. this year he's in a math class and for the first time he's failing. I am at a loss.

he thinks it's because he's just too stupid to do it and I KNOW that's not the case. It's just that this is very tough math. They're combining trig and calc and it's a different type of thinking. we have a tutor, we have met with his school (teacher and principal), we've signed up to pay for kahn academy (which he says doesn't help and he hates). I have people available to call, text, video call... whatever he needs but he's still struggling.

I do not know where to go from here. I'm watching my bright child slowly lose his confidence and spark. it's not because he doesn't try. it's not because he can't do it. I just think there's some tool or teaching style we're missing here.

can anyone suggest something we haven't tried? he's a junior taking senior math and I want him to build back the confidence that he knows his stuff. right now he may have to repeat this class and I think that will devastate him. any ideas would really help.

thank you