I just got a 87 nissan stanza. The car has been sitting for a minimum of 6 months. I started the car up and started driving it and at first it went really good no hesitation or anything. I had to put some gas in the car and after about 50 or so more km it started to bog a little bit. Now it doesn't do it all the time. It will sometimes hit 90 no problem at all. Other times I can't even hit 60 without bogging down. I am going to try and injector cleaner and changing the fuel filter. Any other suggestions?

Its automatic by the way.