Thanks for the thoughts guys -
As far as the Tundra and me selling my truck - yes I sold my F150 in order to get a 3/4 ton truck or something with a larger payload capacity. It was my understanding through ExPo and WTW that Tundras have a much greater payload capacity than my F150 did, and that it is comparable to a 3/4 ton truck. If I was mistaken then I guess I didn't read other member's posts correctly....either way the skinny of it is, Yes, we sold the truck to get a truck that could carry more, or to purchase another vehicle entirely (van, etc).
As far as living in a pop-up - we've gone out and looked at pop up models as well as hardsides. We understand that the Hardside gives you better insulation, and also more room permanently, but it also means that the drag on the truck is greater thereby reducing MPG, also the height will be an issue if we go on back roads with low overhangs, and the weight may be considerably more. With a pop-up we feel like the truck will feel more like a truck even with the camper on the back, and that we will be free to explore as we do already without the worry of denting or tearing up our camper. Not to mention the drag and weight should be considerably lower - thereby not affecting MPG as much. We're not against hard top campers, just not as drawn to them for our needs.
As far as full-timing it - we're young still and of the outdoorsy group. We camp, hike and backpack all the time, mountain bike, road bike, play on rivers, etc. If we're off in the woods, pooping in a hole in the ground isn't a big deal to us. Not having a shower every day isn't a big deal to us. It might be cramped, but we usually camp in a tent smaller than the truck campers, or in hammocks under a tarp - however a very valid point is that we aren't doing this full time, but we have both done it for multiple weeks at a time and never had any issue. Having an actual 'abode' of sorts on the truck sounds like a huge step up!
The other option we keep toying with, and that we had originally toyed with but tossed out since I owned a truck, was to buy a van and either convert it or find one already set up for vanliving.
We scrapped this idea because we had the truck and figured it would be easier to put a camper in there - obviously we had no idea that the truck's payload was barely enough to carry us. So now we're looking for a van to potentially satiate our hunger for adventure.
I actually know several people, and a couple or two who are couples, who are living in their pop-ups or vans and traveling around the country. Most of them don't have porta-potties, showers, etc, but they get by. I think we'll be fine, but I always like to hear insight from other people.