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Verify the firing order 1-5-3-6-2-4. Did you spray for vacuum leaks using B12 or other aerosol carburetor cleaner, including all around the integral intake manifold, carburetor, etc? What procedure did you use when adjusting the valves? Did you verify valve motion on all cylinders? Did you have the cylinder head Magnafluxed (checked for cracks) and rebuilt while it was off the engine or simply replaced the head gasket? Did you run a dry/wet compression check beforehand and after? What were the pressures? Have you checked engine vacuum? What carburetor float level setting did you use to adjust the float?
why did you have head work done? did you have this problem before the head work?
the sensors on your truck should be very limited and none should effect the truck due to not having an ecm. a condenser for the ac? have you tried to remove the exhaust? before you replace anything you should try to eliminate what you can and if that can be done cheap or free then thats even better. unless you have spare cash just to be tossing at the truck