How is lift affected when military aircraft ad weapons and fuel tanks?

Weapons and tanks increase drag index and weight, all of which has to be overcome by increased thrust, to generate speed (airflow) which makes lift. Yes it can be slowed down and manueverability degraded by all that crap, that's why most have a switch or button that will clear the wings. In the Viper we called it the Gross Weigth Adjust switch -- actually it was labeled Stores Jett (for Jettison).