Toyota 4Runner is a very good truck - powerful engine, quiet ride, high quality, and very well made. But you said you were looking for more interior space than you have in your current Blazer, which is one thing the 4Runner just won't really give you. Like your current truck, it's a mid-sized vehicle that was originally designed around a V6. It might be a little more spacious that a four-door Blazer but not by that much.
The Chevy Tahoe gets excellent fuel economy for a full-size SUV. Last one I drove (GM press car) had the 5.3L V8, and cost about $90 to fill from E. For that, I got about 475 km, which works out to something like 15 L/100 km.
By comparison, I seem to recall that last time I drove a 4Runner (also a press car) it had the 4L V6 and cost about $70 to fill, taking me about the same distance. That works out to around 13 L/100 km.
Bear in mind, both of these are brand-new vehicles still being broken in. But you get the idea. There's not as much fuel economy difference as you might think.
If you want more space, you're most likely looking at a full-sized truck of some kind. If you want better fuel economy than you already get, you're most likely looking at a newer mid-sized. Sorry to say, you can't have both in a 4x4 SUV.