Doh! Sorry guys--I should also have noted that there is, indeed, a new coil in the truck. I replaced it the first time it started acting up and the problem seemed to go away for a while. Now it's back. I was so sure it was the coil myself and the replacement seemed to confirm that diagnosis. But now I'm back to square one.

Which sensors should I check?

 

Sensors don't ALWAYS throw codes. That's the problem [&:]

If it idles poorly when cold, check the coolant temperature sensor and the idle air control motor/valve/whatever you wanna call it. It's on the throttle body. They often get dirty or start to fail and can cause intermittant problems.

If those check out good, then work down to the oxygen sensors.

After the oxygen sensor, the ony real culprit (sensorwise) left is the crankshaft position sensor. It acts as the HEP...or the pickup plate for the distributor.

One non-sensor item that can cause idle issues and poor performance is a cracked head. Did you have the heads checked/replaced after you had that spark plug issue a few months back?