sputtering

Started my truck one day.. and was sputtering.. in the past I've changed out the spark plugs n one of them were bad which solved the problem.. but this time.. the problem was solved but came back but only on the low rpms.. until I'm in the high rpms then it seems to clear up or run fine.. any thoughts of what it could be b4 I start buying all kinds of parts?! Mahalo!

How many miles are on the engine? I would suggest doing a compression test to rule out a burned valve. If your engine is fuel injected then maybe you have an injector that is getting flaky