The longest trip I ever did, as a kid, was about 8,000 miles. In the summer of 1982, my Mom had a 6-week workshop she had to attend at Shepherd Air Force Base in Texas. (oops, just googled it, turns out it's actually "Sheppard"...I've been misspelling it all these years!).
Anyway, my grandparents decided to plan a vacation around it for them, and me. We left out of Glenn Dale, MD, on a Friday afternoon in June, and went down to SW Virginia, where my uncle was living at the time, and dropped off the dog for him to watch. Then, we took our time going out to Sheppard AFB, taking about 2 weeks to get there, and stopping at various sights along the way. The main things that stick in my mind were the 1982 World's Fair in Tennessee, Mammoth Cave in Kentucky, the highest point in Arkansas, and another place in Arkansas where you could pan for gold or diamonds or something like that.
After we dropped Mom off, we took our time going West, with the final destination being Grandmom's brother and sister-in-law in Long Beach, CA. At the end of Mom's 6-week class, we arrived back there, on a Friday evening, and then I remember them booking it (as we said in the early 80's) to get back home.
As a kid, it seemed kind of unreal, that it took us two weeks to get from our house to Texas, but then going home, it took about a day and a half. And that was with stopping back in VA to get the dog, and resting up and visiting friends for a bit, and then heading home.
I seem to recall the trip was around 8,000 miles, total. My grandparents had a '76 GMC Crew cab 3/4 ton pickup, with a slide-in truck camper.
Nowadays, the idea of getting to Texas in a day doesn't seem like a big deal. But at the time, I was only 12. Prior to that, the only somewhat long trips I'd ever taken were to Florida. In those trips we usually left early in the morning and drove through the night, and would get there early the next day. That was about 1000 miles, versus maybe 1500 for Sheppard AFB. But, for some reason, as a kid, Florida didn't seem that far, where Texas seemed like a whole different world!
On my honeymoon, we drove from Maryland out to see her relatives near Seattle. Made the trip in 76 hours. It had its ups and downs, but I don't think I'd ever want to try driving across the country that fast again. I'd rather stop and enjoy the sights along the way.