Warranty repair question

[Cazador]

My check engine light came on today when I started the truck. Drove it down the block and it seemed it had about half the power when I pressed the accelerator. Turned it around and put it back in the garage. The check engine light is solid on, not flashing.

My dilemma is whether to tow it or drive it to the nearest Hummer dealer. Closest dealer is 153 miles away. I talked to the Hummer dealer and they say "drive it", but the distance worries me. I asked them if the local GMC truck dealer could perform warranty work and gave an emphatic "NO", which I find ridiculous...

Tow it, drive it, or diagnose and fix myself(If i were a betting man I'd say O2 sensor)?