UPDATE:
No tachometer, but I did discover and ask about the two "D" on my gear selector and my mechanic told me plain D was drive like around the city, the D with the circle around it was overdrive. Not that I used the plain D at all. Well I am one of those people reads the manuals cover to cover but my used GMC came with no manuals. I been finding new stuff ever since.
OK. It does downshift well with no load. Mechanic said he took it out and got it up to 75 mph on the freeway piece of cake, smooth as silk. But he said he did see the antique catalytic converter under there said the old kind with "beads" and could be choking the engine. So he will remove the cat con and also replace the fuel filters.
When I get it back I will take it down to be weighed as it is now fully loaded to go and will report back. Thanks everyone.
