I have a big Better Boy tomato that's been hanging near the bottom of the plant for two months and it is still immature green. A few that set after it, or at least above it, have been harvested and eaten. I don't think what you've described is unusual, just taxing on the patience. I've read tomatoes stop ripening, or perhaps lycopene stops forming, something like that... above 90 or 95 degrees. I have noticed almost no change in my tomatoes during a long hot day, but often wake in the morning to blushing fruit. They went through positive changes overnight while the temps cooled. Just hang in there.

I will add this about Better Boys since I've grown them for almost 20 years. In mild climates they seem to be much tastier than out here in the desert. It could be how dry it is here in addition to the heat. I've been reading bad things about that. It was 105 and 2% humidity yesterday at 5pm here. My Better Boys taste watered down and the skin is definitely thicker and tougher out here than in LA, where I grew them for years without really knowing about all the variety out there. I have 12 of them in the ground in three different locations so I think I have a good feel for how they will perform in my heat and I'm not impressed. I have about 10 pounds on the counter I've decided to turn into sauce. They were planted earlier than Champion and Red Beefsteak, set fruit before both of those too, but they are in most cases much slower to ripen, just like you're experiencing. To my surprise they are much more susceptible to cracking than my other fruit too.

I'm typing all this because Better Boy has long been my favorite, but that has to change given my extreme conditions.