stumble/hesitation

I have a '99 Silverado extended cab with a 4.8 liter engine. At times it stumbles and hesitates. This morning I had to tap the gas pedal to get it to start and then it seemed to surge untill it got running on it's own. This problems started about a month ago and right before it started to do this I put in a new K&N air filter, changed the plugs (autolite platinums), changed oil/filter and changed the fuel filter. I have spoke with some colleauges and they said that the oil on the K&N filter may have messed up my mass airflow sensor? The service soon engine light has never came on so I myself doubt this. Also had a friend say that the fuel pressure regulator might be going out too? The truck has about 67K miles on it. I am leaning towards the fuel pressure regulator as the cause, what do you think?

Sounds like it, Pull the vacuum hose off of the regulator and see if there is gas coming out of it. If so it needs a new regulator, I replaced bunches of them.