You're drunk. If you could swap the current 5 speed with a good 8 speed like FCA is using in the Rams, and gear it properly, you'd be looking at another 2-3mpg with better performance.There are no real world benefits whatsoever to 8-10 speed auto transmissions.
A V6 Grand Cherokee with the 8 speed gets a good 20% better fuel economy than we do. A V8 Ram quad cab with the 8 speed can get about the same. That's in heavy pigs with thirsty FCA motors.
10 isn't necessary but 5 to 8 has real benefits.