My wife and I traded in a 2wd short-bed, reg-cab V6-5spd Silverado 1500 with 185k and a Hyundai Santa Fe with 200k on an '06 Sequoia 4x4 (the SUV version of your truck) with low miles. After driving it around a bit I understand your passion for that truck. I've had a few trucks mini and half-ton. I also had a 2x4 '92 Toy 22re/5spd which I bought w/110K (for $700.00) and sold with 220k (only because the head cracked out and I couldn't justify the $$$ for a 2x4). I miss that truck dearly as it was an awesome motorized wheelbarrow. I would NOT sell your truck as you know it's history and (I assume) it's in good order. I am in the process of doing what others have mentioned and am buying a '93 4x4 S10 4.3/5spd ext cab. When I'm done it'll have a one-off flat bed, lift, rancho shocks and good tires. It will not get much worse (or better) mileage than my 4x4 '02 F-350 Powerstroke CC/LB dually with a 6spd trans and 4:10 gears. It WILL be cheap to tag, insure, and fix. It will also go places that the dually will not or should not go. If you get a 4x4 mini truck, the mileage won't be much different than your SR5. It will offer less and more though.
I guess after that rant, I would say don't sell your truck. If you really want a small one, buy one right and laugh all the way to the bank. It will compliment the one you have now. think of it as the 50cc/70cc saw plan in trucks.