The "tonnage" term has become so muddled, who cares? All the marketing hype is about towing, not payload capacity anyway. GM has 1500"HD", Ford has an F-150 "Payload Package", and I dont even know the Ram (not called Dodge anymore) offerings.
Emissions rules change at 8501 GVWR which allows for diesel engines. The mid 20th century definition of "3/4 Ton", which was 7500 GVWR is long gone. Unless Toyota has a suitable diesel engine that meets or can meet US regs, its probably not worth it for them.
The only physical size that matters to me is the bed. An F-150 and F-350 have the same basic dimensions, as does the Tundra, Silverado/Sierra and Ram. A 1960's F-100 may look pretty wimpy sitting next to any modern truck, but the same size stuff fits in the bed.
Toyota and Ford cross-licensed hybrid technology quite a while ago. Maybe they are developing a hybrid truck package together.