We have a 05 F350 DWD 4x4 long bed with 125K miles, its bullet proofed, not because we had to, it's because we wanted to since we are pulling a 12K trailer out here on the left coast. :B
The way I look at it, it's not how fast you can go, it's how well you drive that makes the difference in how well the truck preforms. I go ever most 6 percent grades 10 or more miles long between 45 and 50mph, I go down those grades at 40 to 45 sometime slower.
My old truck has proved me and the DW & our 2 dogs safe an fun trips up and down the left coast an into the heartland of America, give us a wave as you pass by please...
Safe travels and we will see you down the road :)