I can't say anything about the GM6.6. M last chevy truck did very well for about 125k miles and I traded it cause in Texas I don't need 4x4.
My current F150 has 110,000 and I am truck shopping. I really like my XLT, with the 32valve 5 liter "Coyote" motor. I can pull 8000 easy and it doesn't seem to work hard at all.
I've been looking for a 3/4 ton, long bed, not a four door and not 4x4 and have not found anything at all.
But I am going to look at a 2020 F150 3.5 twin turbo with a 11000+ lb Max Tow Package tomorrow. With incentives it is right at $40k. With luck I will get $15 for my trade and be very happy.I am also going to look at a 2020 RAM 1500 also with a 11,000 lb tow capacity. It's a little more money but a much nicer interior, kind of like a Lariat in the Ford.
I'm kinda glad I could not find a big truck as a "heavy half ton" is a better daily driver.
EDIT: if you do get her the boobs, make sure you get visitation in the divorce.