SES light wierd problem

I am having a strange problem with my 97 tahoe 5.7L. It misses bad when you are driving down the road until you get to highway speeds and then it isnt as noticable. But the wierd thing is while it is doing this there is no SES light. Then as soon as the SES light come on it starts running perfect. I had the code cleared which was a random misfire and it started missing again. Then as soon as the SES light came on it started running fine again. I bought it in Feb of 06 and replaced the distributor cap, button, wires, plugs etc and have only put about 7000 miles on it since then. Does anyone have a clue what is going on with my truck? THanks.

Retrieve the error code(s) and you should have a hint of the problem. Just a WAG is that it might be related to intake airflow.