Those older campers didn't weigh anything compared to new ones. It's got no roof air, no jacks, no generator, and I bet you even let your kids ride in the cabover. I don't even see where your tires are squishing. Ahh... the good 'ole days.
I had 12 foot (not even 11 1/2--a real 12 foot) Real-Lite with the side door entry on an F250, completely stock suspension, and it didn't squat. I also loaded a boat behind it, and at that point the truck sat pretty much level.
Those older trucks were over built, and the campers were much lighter.