I live in CA (I know "move to a better state") and my truck just failed smog, twice.

1st test:
NOX levels at 15mph measured at 1154ppm
Max: 992ppm

NOX levels at 25 mph
measured at 358ppm
Max: 596
-- checked EGR, replace thermostat, replace PCV Valve, check for vacuum leaks.

2nd test
NOX levels at 15 mph
Measured: 1110ppm
Max: 992ppm

NOX Levels at 25mph
Measured: 1079ppm
Max: 596ppm

Just by replacing the Thermostat and PCV Valve the levels went up by 721ppm at the 25mph benchmark.

Wtf?

 

I would start by checking ignition timing and carburetor adjustment. You said you checked for vacuum leak. Also try clamping the hose to the brake booster with a pair of pliers. Check and make sure the EGR valve is not sticking open. You might try spraying brake clean around the intake manifold to check vacuum leak. hope this helps. newtjr

 

spike the reg gasoline with straight methanol, 30-40%. it will run like crap, but should pass. or use E-85. OR make a secret propane injector. all so the experts here can give advice on what the engine temp should be.