I really depends on how much you want to replace. If you currently have 2.x gears (series 2 carrier), you may need a new posi carrier or to use a spacer which many frown on. Since it's a Z28, it should have 3.xx gears, but make sure before you order. Most people don't go above 4.10 for street with the 4L60E or T56, but you can go more. Many think that 3.73 is perfect for the 4L60E while 4.10s for the T56 in 4th gens.
Be careful with a higher stall if you have good traction. The rears in these cars are not that strong. If you have a stock Z28 with street tires, you should be OK.
You didn't say what your other mods were, but I did a LT4 cam, CAI, headers, exhaust, and a tune. This really woke up the car - super quick. Now I'm looking to put in 4.10s, but I already have 3.73s with my M6.
Oh yeah - don't forget that with new gears, you will most likely need to re-program the PCM.
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