dont forget the batteries truck is heavier than a standard one.
fair enough most trucks max out on volume before max legal mass, but that will be a consideration for some.
By the time you have added a generator, a fuel tank a transmission, an exhaust and a cooling system you will have
A added even more weight
B taken up even more space
C added even more cost.
D started to make weight and load space an issue for everyone
Basically adding an engine to it is a stupid idea, if it wasnt Tesla would have added one.