As i was reading in the search i came along both of these options. Now i will be putting the zz4 crate motor and as i have learned the t-5 can't handle it. So i figured t-56 but i also learned about the g-force t-5 up grade kit that can handle up to 400 or 600 horsepower. I was curious what would be better for my engine, the zz4 crate engine, and was curios t-5 rebuild or t-56 retro fit?

I have the retrofit T56 and I am pleased with it. One thing to consider is that with the T56 you will have two overdrive gears, so you can run lower gears and still maintain decent rpms cruising at highway speeds.

rather then a beefed up T5 or the retrofit T56, i like the stock LT1 T56..... *shrug*

i would go to the t56 but keep in mind you will probably want to go 3.73 or 4.11 to off set the taller first gear.

The aftermarket T56 is geared numerically higher than the LT1 T56. I think the first 4 gears are similar to the T5 gear ratios, but double check on that. I know first gear is roughly 2.97 vs. the 2.66 1st gear in the LT1 version.

If he already has a T5, the aftermarket T56 is pretty much a direct swap. It only requires cutting back the torque arm 2", which can be done with a hacksaw or cutoff tool, and having the driveshaft shortened 2" (cost me $40).

I'm not saying that you shouldn't go with the g-force T5, I just have no experience with that transmission.