personally, i dont advise using coolant stop leak products. how well have you checked for leaks? i did my intake gaskets, and after about a week, a clamp loosened on a small line on top of the water pump. as a result, i have a small leak, that i just havent had time to fix. the coolant usually burns up on the engine or water pump before it hits the ground. i RARELY ever see any kind of spotting on the ground.
can you smell coolant when the engine is running? if so, is it right away, or after the truck has warmed up for a while? make sure all oil and trans coolant lines arent leaking.