[jlmerie]

I also live in Colorado. I have a 1978 GMC short bed truck. It is a 2 wheel drive and rated at 6050 GVW. Last time I was at the emission testing station for my Jeep, I talked to the station manager about what emission equipment I needed for the 78 GMC. We concluded almost nothing was needed. NO catalytic converter was needed. The truck also did not have any designation for unleaded gas. That is the fuel gauge in the dash did not say "Unleaded Gas" and the gas filler tubes did not have the unleaded restrictors. I agree with Ray that the cutoff for heavy duty was 6000. The fellow I talked to got out his reference books and confirmed this information for me. I have to believe the emisions would be about the same as 1977. Certainly 1977 would not be more restrictive.