starter problems???? I think

[pissonNOS]

been cruising last 2 night in a row and when i shut my truck off it wont start after unless i get a boost. So saturday i checked the charging system and everything turns out ok there i had one loose wire on the alternator i fixed. after i had all the charging fixed and it still wouldnt start i tapped the starter and it started fine. now i have not been cruising all day today (sunday ) and the truck is running fine and starts everytime. anyone know what this would be ? maybe because its so hot out?
thanks