Thermostat set at 75 but showing 65 in the house heat will run but turn off not reaching what is set on thermoststat turns off for 1 minute and turns back on not heating to maximum.

Does it feel 65? Could be that tstat is out of calibration, or bad. Get another thermometer and hang on wall beside the tstat compare the 2. you might bypass the tstat for a while see if the furnace runs continually without cutting off,if it does run fine you will know its not the fought of the furnace

Post brand/model# of indoor unit. Heat pump system? Perhaps the outdoor unit isn't running? Thermostat not level, if mercury-type? Gas furnace? Status light blinking, if present?