The most accurate method is to weigh your TV with your rig hitched up and determine how much weight your rear tires are supporting. Go to tire manufacturer's website to view recommended pressures for the weight your specific tire is carrying.
My E-rated tires can easily support the weight of our rig so I inflate mine to a bit over 70 psi as max 80 psi provides too harsh of a ride, front tires are set to 60-65 psi. The ST tires on our rig are set to max pressure as stated on sidewall as ST tires perform better at max pressure.