I'm taking down the DEF tank on a 2017 Diesel Colorado in order to gain the clearance needed to replace the rear shocks and I've hit a couple snags due to corrosion.

The tank is mounted on posts/studs with nuts which hold the tank in place. One such stud and nut on the rear of the tank seems to be spinning freely without clearance above to anchor the stud and work the nut off. Another stud on the front side of the tank is welded to a cross bar above and is threatening to snap if I keep pushing my luck muscling the nut.

What; are the tricks in getting these nuts off without doing damage to the studs?