If u have to hold ur gas pedal to the floor to start ur car then u probably have a bad coolant temp sensor. It's screwed into ur head below where ur upper hose goes on to the head. There's two wires going to it a black one and a yellow one. Make sure u check the connector for corrosion if it's corroded u will have to replace the connector too. Make sure u get a brass tipped one the plastic tipped ones crack. As far as ur coolant leak goes I wouldn't use stop leak or pepper never heard of that one.I can't tell u where it's leaking but I can tell u the most common spots they leak. Look where ur top radiator hose goes onto the radiator right below that where ur transmission cooler line goes on the radiator cracks there on the tank and leaks. Another common place is the water pump leaking. Other then that u would have to have the cooling system pressure tested or add leak dye. Let me know what u find.