Yes it does.
Transmission gears? In the transmission.
It could be anywhere from five to 18.
One the 1999 and newer trucks, some 2WD ext cabs and 4WD ext cabs with the 5.3 came with 3.73 gears. Others came with 3.42 gears
Yes
A typical mixer truck usually has between 5 to 10 gears, depending on the specific model and design. Most commonly, these trucks are equipped with a manual transmission that allows for better control when maneuvering and transporting concrete. Some modern mixer trucks may feature automatic transmissions, which can also vary in the number of gears they have.
Certain trucks, particularly those designed for specific tasks like light-duty pickups or certain commercial vehicles, may not feature extra gears. These trucks typically have simpler transmission systems optimized for efficiency and ease of use rather than performance or heavy towing capacity. Additionally, some economy models prioritize cost-effectiveness and may forgo additional gears to keep manufacturing simpler and more affordable.
There is no maximum. The manufacture could theoretically put as many gears as they want. Mercedes Benz has a 7 speed transmission & Chrysler has an 8 speed transmission. Long haul semi-trucks have 26 gears ratios or more.
Specifics for European trucks, I'm not sure about, but universally, the manual shift transmissions will be unsynchronised, consisting of anywhere from 8 to 18 gears total, although synchronised gearboxes with just five, six, or seven gears are often seen on single axle straight trucks/rigids. There are also automatic transmissions available, as well.
How much weight it can tow or carry and how much you need it too. How many gears it has and how easy it is to steer and shift.
If you're talking about the differential gears, 75W-90 is something of a default for medium- and heavy duty trucks.
In a true automatic the gears are applied and released by hydraulic pressure, usually in a special oil. The control system is either an analog hydraulic computer (called a valve body) or on newer cars and trucks an electronic computer that controls the hydraulics.
For a North American truck, most of your average fleet trucks will run either a 9 or 10 speed transmission. Owner/operator and heavy haulers tend to have more gears - 13, 15, or 18 (15 speeds are a bit uncommon, though).