Just thought I'd post this here for anyone thinking about a regear.
My truck had a 3RZ with a 4.10 rear end so I regeared up to 4.30 using the third out of another truck. Easy as pie. Remove the axles, unbolt the third swap the new one in. I didn't do any shimming since both rears were set up and I just swapped housings. Man did that little bit help. Acceleration's improved. Pullings improved. Gas mileage has even improved around the city. That's with 31x10.5 Goodyear Wranglers.