How much does kenworth t660 weight?

You didn't specify if it was a daycab or a sleeper, 6x4, 6x2, or 4x2, etc.
I worked as a mechanic for a fleet which used to be predominantly made up of T660s - they had either the Cummins ISX15 or the Paccar MX13 engines, and all had the FRO16210C transmission (10 speed). They were 6x4 with 40k rears and a 13k front axle, and had the 72" Aerodyne sleeper. I don't recall off the top of my head what the exact wheelbase is. All trucks used aluminum rims all around, and 295/75R22.5 tires. They all weighed between 17,000 and 18,000 lbs. Exact weights will vary according to specifics, e.g., engine, transmission, axles, other features, etc.