No comment on the grill removal but when you install your additional cooler make sure you have it installed After the Radiator in the coolant flow.
Often manufactures install the cooler before the radiator relying on the radiator to warm the transmission in winter. This limits the overall cooling to that of the radiator temperature and the aux cooler just clips off very high temperatures.
On my system I bypass the transmission loop in the radiator and use a fan driven cooler with a thermostat set at 165 degrees and them to the factory cooler.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles