I'd avoid 4WP at all costs...they sell only genuine gear, which is well known in the gear world as the worst money can buy. Don' t be swayed by the "lifetime guarantee," since you have to pay for labor. I got Precision Gears installed at drivetrain direct in Corona. They are a distributor for superior gear, but I insisted on Precision since I've heard only good things about Precision and US Gear (I think precision makes V6 gears...you definitely want V6 gears. DO NOT use 4 cyl gears and shim them, which is what many shops do). I've heard mixed things about Yukon, Superior, Richmond gears. I think Yukon and Precision are the only companies that make V6 gears (I might be mistaken...check their websites).

Whatever you do, get the work done at a shop that specialized in diffs. The guys at Drivetrain Direct do installs every day...there are two guys that do the installs (at least the day I was there). Otherwise, there's West Coast Differentials near Rancho Cordova.