the only thing i can think of is the truck doesnt have enough power to get things going. my truck makes a sound that is kinda like wut im picturing yours is making when i dont give enough gas when starting on a hill or something. the truck has just enough to get going but you can hear it complaining.
id recomend going out and getting the fuel system cleaner and the oil system cleaner. can be found at wal-mart and auto stores.