So i have a hard top coolant hose after I shut the engine off. And when I go to the resovour coolant tank to cap off I gear a hissing sound and then all the coolant from the top radiator hose goes down. Please just tell me all ihave I a bad resovour cap. Any help is great, thanks in advanced.

Do you see any visible leak? Like in the morning below the truck? Also check when it is running.