Oh I feel ya bro, winter is the only time I can control the heat in my house. The AC just doesn't do what I need it to do in my grow room in the summers here in Illinois. It's just a hot and humid hell, and I'm always fighting temps. I've had so many problems stopping my PC over heating, I had to use some MacGyver tactics of my own lol.
Looking at your setup, and with it being in the garage n all. I would add a 10 - 15 foot length of duct tubing to your "intake" fan. Making it pull the air through a lot of coiled aluminum tubing, it will drop the temp of the air down about 2 or 3 degrees on the front end, shaving off valuable degrees of heat on the back end to keep you nearer 80 degrees, than it climbing to 90 degrees, which can be a plant killer.
How are your insides of your grow box finished? Do you have foil on the sides, or bright white paint? If the air inside is touching painted wood, it will insulate the heat and build, if the air hits the foil inside, it will reflect and dissapate the heat a little, not by much, but every little bit helps. You could also paint some kind of light reflecting (white) sealer on the cabinet outsides, to stop it absorbing even more heat. Make it look like a fridge. Touch a white car in the summer compared to a black one, it's several of degrees of difference.
I have a 3x3 tent, but I have my own grow box too. When you can smoke some bud from a MacGyver setup, that's called 'surviving in the wild' as far as I'm concerned lol.
Also if your light is generating the heat, having a fan blowing directly on the light itself can keep it from building. Sorry if you've tried all this before, just covering the basics.