Could be a bad connection at your MAF sensor. The wires get very brittle and may cause a bad connection. I would unplug your MAF and see if it runs any different. GM makes (or used to make) a pigtail connector for it. Also if you don't have a check engine light scan to see if there are any pending codes. If its intermittent it may not cause the light to come on, but may be enough to store a pending code