The family vehicle is acting up(1998 suburban vortec 350). It seems like a gas issue but im not for sure. This thing putters and putters. The more you get on it the more it putters. The service engine light is on. I put some fuel injector cleaner in it about two weeks. It putters a little in park but very badly once in drive. Changed the fuel filter about a year ago(inline, what a *****). Where do I start in getting her to running better/normal?