I don't claim to know the answer for sure, but I think it's a combination of things.
When regeared it would take less torque for engine and tranny to turn the driveline, which in turn means less TC slippage at startup, and you can now use OD on the freeway (no TC slippage in OD). Also, the engine can now run at its best, most efficient, and most powerful rpms during taking off from a dead stop and also on the freeway, thus saving some strain/lugging on the engine and saving some gas too.
I think the above is correct. Won't swear to it.
Lastly, if you have the auto tranny (like I do), its a sucky tranny IMO. My biggest complaints with it are the OD is too high. There is too much gap between 3rd and 4th, which makes it really easy to lug down in OD. Also, it shifts to OD at to low of an rpm. Lastly, the OD might be just to high geared period, though I get by using the OD button to manually shift from 3rd to 4th.
Hence your questions about how did the regear really help. Additional reasons why I think you wonder if it helps is that it only helps in some situations, but not all.
My answer is that it did help you a lot for taking off in 1st gear, and it may have helped you somewhat for cruising on level freeway a bit faster. For cruising uphill on the freeway it didn't help you a bit and probably hurt you (IMO) because now 3rd is to low for freeway hills and 4th is still to high, if your auto tranny is like mine.
I keep the OD turned off until I reach 2600 to 2700 rpms in 3rd (on level freeway), and then I manually upshift it to 4th by pushing the OD button.
Someday I'd like to install a tranny kit that makes it not upshift to 4th until at 2650 rpms in 3rd. Also, I'd like it to wind up the rpms a little higher in the other gears, before upshifting. That would cure a lot of problems that regearing helped, but regearing alone cannot cure. In the meanwhile, until I can afford a tranny kit, I'll continue manually upshifting from 3rd to 4th by use of OD button.
Anything I do can only hope to improve the situation. It will never be fully cured because the OD is to high geared for the 4L engine, even with stock tires, and moreso with my 33" large tires.
Would the high OD be nice with a 4.7L stroker, 33" tires, and 4.88 gears? Maybe. I think it might then be nice.