I've been down that road, trying to pull too large of a trailer with not enough truck.
after air bags , tranny cooler, stiffer sidewall tires, and a rift of other mods, I still didn't have a rig that could do the job I wanted it to do so I just bit the bullet and upgraded to an out of the box truck that met my needs.
when you're shopping for a trailer don't listen to the crap the salesman spews about your half ton being able to handle the load you're going to be putting on it, he don't have drive the damned thing. if it comes down to making the sale or not, he'll tell you anything it takes to make you sign on the dotted line.
as far as having the 9ft. garage, it'll be tight but can be done.