2002 Dodge Dakota tapping sound

I just starting hearing a tapping sound which sounds alot like a lifter. At first I would only hear it when my truck would get up to about 45 mph or getting on to a freeway onramp. After about a week its been getting worse and now I hear in every time I excellerate. I checked the oil and its good. When I first bought the truck brand new I had a similiar problem with one of the tappets and the dealer had to replace the lifter and cyllinder under warranty thank God. Now the warranty is no more and I'm nervous about taking to the Dealership in fear of getting railroaded. Do you think it could be something more serious than a lifter adjustment? Also do you have a recommendation on a good oil to use? I keep seeing synthetic is good for this kind of truck on the Dodge Dakota website.