1988 GMC with 3406B CAT - Estimated Fuel Mileage?

Depends on state. In Arkansas you have to run a Natural Resources plate with logs

 

I don’t know much about your business, but this was the most reliable engine I ever had.

 

Not much. That poor thing... it's going to be a real hassle to get it lubed up, fresh fluids and chasing over corrosion in your wiring etc. Oh that poor rig.. Take a hammer and beat in the frame you will have thousand pound of rust come off there. //snarky.

Batteries will have to be put in, wheels pulled to see where your bearings are (If any present) and so on. It's been left in the field too long me thinks. Every time I see a truck like that rotting away with a forsale sign on it, I think it will cost me upwards of several thousands of dollars to do the whole thing from to back.

 

I’d go for it, sounds like a great deal. Drivability of th 425 is excellent. Fuel mileage will depend on your foot. Should be able to get 6 or better, if you watch it. Best part, it will be consistent loaded or empty, less than .5 mpg difference. Due to good torque. Fuel pumps can be an expensive replacement/ rebuild. Best to find a good Cat mechanic. If there’s any left. Lol You’ll Love Driving it, great power, better than a 500 Detroit. I think rods and mains recommended at every 250 k on that engine. If I recall correctly, something to check into, anyway.

 

My question is what was your road speed?

 

In Most states, if not all, they go by the GVW tag.

There should be a gross vehicle weight tag either in the door jamb or maybe up by the kick panel.

Some states allow more weight on a tandem some allow less. Here in Pennsylvania is 58400 if you have heavy enough axles for that. I think there are other states that you are only allowed say 52 or 54, and some states it's probably more than it is here. In New Jersey tandem dump trucks I think run 70,000 if the axles are heavy enough.

There is no state that I'm aware of you can run a tandem at 80,000 lb. That might be the gross combined weight meaning he maybe pulled a trailer and the combination was 80000 lb.

I think most if not all states you can register the truck for less weight than what the GVW tag says, but you can't register it for more.