4LO is geared very low, but delivers so much torque to the wheels that you could almost literally pull a house off it's foundations. Of course you are really revving the engine high if you try to drive more than 10mph in 4LO, so unless you are stuck or pulling someone or something else that is, stay out of 4LO. 4HI is used when on gravel, snow or other slippery surface when traveling at normal speeds, like driving to work in a storm or trail riding.2004- wouldn't it have been a Trailblazer by then? Not a huge difference, but I think they are somewhat more advanced than the older Blazers you were looking at previously, aren't they? As for securing stuff, the best idea is to maybe use the tie downs that are found in most trucks and some high quality strapping to hold a tool box down. Also, if you can find a tool box with a wider, flatter bottom instead of a taller one, it might help keep the center of gravity low.One idea I had long ago was to build a "second floor" in the back of a truck. I may still do this with my Jeep, but it should also work nicely with a Blazer. Build a frame on either side of the body tub, about even with the tops of the wheel wells, making sure to include framework that fits in between the wheel wells. Attach some heavy duty drawer sliders and a box to the frame and cover the whole thing with plywood and new carpeting. What this will mean is that when people look in the back, it will look like regular flooring, but when you open the back end, you have a large slide out drawer with all your tools, jack, fire extinguisher etc safely tucked away underneath. I figure all you'll need is a level, drill, maybe a reciprocating saw and a rivet gun to do the whole thing- and some 1/4" plywood and galvanized steel L shaped, all of which should be available at Home Depot, and cost maybe $100, but probably less. The only reason I haven't done it yet is I'm trying to figure out a way to keep the back seats. Of course, the Blazer has a much larger cargo area than my Jeep, so you could easily do it behind the back seats and not worry about it.Def