To continue my saga to pinpoint why I've been getting 9.5 MPG lately (both the DIC and 600 miles of calculation correspond), I ruled out sticking brakes using an infrared thermometer to check the caliper and disc temps and all were fine.

Now I'm thinking it's a fuel leak (xover tube?), bad O2 sensor, leaky injector, or a defective block allowing gas to seep into the crank.

Since I've confirmed the DIC is actually correct, the computer must actually be injecting this much gas into the engine. I can therefore rule out fuel tank leak, defective block/rings, and leaky injector because otherwise the DIC should be on the high side? What's left? Bad O2s? No codes have been set, other than Service A/H.

Z is out of warranty and is completely stock, save zip tie mod.

Any help greatly appreciated.