It sounds very much like the vehicle has gone into limp-home mode. This is a self-preservation system whereby the engine and drastically reduces the power it’s producing, limits top speed and often locks the transmission into a low gear. Something has happened that has caused this, and a common reason is that something in the engine, fuel system, or (more likely) the transmission has started to get too hot with the strain of towing.

With luck, full operation will be restored once the vehicle has been allowed to cool down. But you may need to visit a dealership to have things reset. It’s always a good idea to do a full engine and transmission fluid and filter change after any overheating event anyway.

It’s not a problem we’ve heard of occurring in huge numbers, but like any component, a canopy is subject to wear and tear just like any other. Canopies on tradie-trucks can cop an awful hammering at the hands of their owners and damage is inevitable in such cases. Even a few years exposure to Australian levels of UV radiation can cause a canopy to start to break down structurally, so they generally have a finite lifespan.

But instead of replacing the whole canopy (assuming it’s a fibreglass one) it might be worth asking a fibreglass specialist (say, a boat repairer) if the crack can be repaired. That would certainly be cheaper than replacing the whole canopy

Isuzu lifted the warranty on its vehicles to six years/150,000km for all utes sold after May 1, 2019. Unfortunately, it sounds like your car was on the road in 2018, which means it was covered by a five-year/130,000km warranty. Although you haven’t yet covered 130,000km, the vehicle is more than those five years old so, technically, the problem is not covered by warranty.

However, I think it would be worthwhile contacting Isuzu Australia’s customer service division and pointing out the car’s service history and its mileage. Isuzu may then decide to help with the cost of repairs on a pro-rata basis given the circumstances. It is not obliged to, of course, but it’s definitely worth asking.