87 pickup poor mpg, good torque

Recently bought this truck and had to have the carb "adjusted" to pass
smog. However, the gas consumption is still awful. From what I can
garner from this group, I wonder if its the 02 sensor or the catalytic
converter. This is because there seems to be faint oder of something
burning or that is hot or something as I am driving for a while and the
engine gets warmed up. It is just a faint smell, though. That is why I
suspect the catalytic conv.

In any case, I need to check this out. What is the procedure for this.
My mechanic said ," if it passed smog in CA then your catalytic
converter or 02 sensor are probably fine."

What should I ask a different mechanic to check for and what should
they charge to check this.

Also, I am considering buying a decent carb but want to isolate the
issues first.

I need someone I can trust to check it out. I am not sure what to
expect or what to ask them.

I can do work on the car but am getting to old and sore.

Thanks