Most over the road tractors are 18 or 13 speed manuals in the US. Not sure of the trans opl change capacity.

Generally the engines are straight six diesels, 10-16 liter displacement. There are a lot of factors for mileage but it ranges from 5 to 8 MPG.

Generally you get anywhere from 20,000 to 35,000 miles between oil changes although Cummins offers the "Centinal" system where you never have to change the oil.

Not sure on the differential oil or coolant capacities. These really depend on what configuration you are running

Fuel tanks run anywhere from 75 gallons to 200 gallons (twin 100 gallon tanks)

Oil capacity is anywhere from about 28 to 45 quarts.

Tractor curb weights are 14-20k lbs unloaded. I'm not sure what the trailers weigh. It really depends on what state you are in on how much you can legally carry. Generally, tractor trailers max out at 80k lbs. But some states allow you to carry 120k lbs. This is why you never cut trucks off...those weights are hard to stop.