Pour that little bottle of Kseal in the overflow tank and take the truck for a decent drive so that it can set. If it's only a small piece of the gasket that came loose, it may hold for a while and you can work on the other stuff while saving up for head-gasket re-work. Now don't hold me to it, as my head-gasket leak was external and quite small. If there is a crack in the block or a liner that is slipping then a gasket sealer may not do anything for you