3406E HP ???????

with Cat ET you can change engine power rating but you need to know ECM password. look for dealer who says that can do it.

 

The highest you'd want to uprate this would be a 375hp, since you sold it............you don't have to worry about it being a pig anymore. Bad choice for an engine working 80,000+ lbs

 

you'll feel 50hp gain. for fuel saving with not too heavy trailers torque is limited with software, as I remember something about 1100-1300nm, with 375hp rating torq. limiter is about 1500-1600nm, but truck is much faster becouse you will get not so many shifting with speed loose. But MPG may be lower a bit....