Took the boat to my parents house to put some rails on it and other goodies. About 100 miles round trip. Truck had plenty of power to get it up and moving and easily maintained speed in 7th gear. Its still not fast by any means, but the 8 speeds are much more appreciated with the load than they are empty. Didn't check the fuel mileage as it was only 100 miles, but the instant readout fluctuated between 15-17 mpg while towing.
Outside temp was 81 degrees and the trans temp would run the same after I reached cursing speed and the oil and water registerd 5-10 degrees over normal which I hear is normal.
Only gripe is with the reverse gear. I read that the reverse gear is equivalent to the 2nd forward gear in ratio... when it came to backing the boat up my folks steep driveway I was turning 2k rpms in reverse... that sucked. Boat is 24' long and as far as boats go I feel its pretty heavy.