96 Sub tune up

I have a 96 suburban with around 141,ish miles. I noticed that the mileage has been falling off. Any Ideas on what I should replace on a tune up.. Also heard of cleaning the MAS? Does this help? Thanks for any help....

If it has some sort of aftermarket air intake like a K&N then the MAF(mass airflow sensor) could probably use a cleaning. Be extremely careful when doing so. Use something like lectra-motive cleaner. I think that is how it is spelled, I use it all the time but never look at the bottle. Otherwards I would change plugs, maybe wires if they have never been done, cap and rotor, fuel filter and air filter. Also maybe a good fuel sytem cleaner. I recommend BG, I sat through a seminar from some BG reps and have used their products on customers cars. Good stuff.