do i really need a shift kit

[ProStreet R/T]

Do you NEED one? nope. But they are nice. And the guy saying they are hard on the driveline is a moron. The basic premisis of a "shift kit" is to not only make it shift firmer, but quicker by reducing overlap between gear changes. A quick explination. To make an auto trans shift all nice and smooth, they begin to engage the next gear before the first is fully released, this is the case for the 1-2 and 2-3 shift. So actually installing a shift kit will reduce wear on the internal soft parts (clutches, bands, etc.)

Yes the firm shifts are a little harder on other components, but really, if you break something cause the trans shifts a bit firmer it was needing to be replaced anyway.

Are you wanting to raise/alter the shift points at all, or just firm it up a bit? I'm more of a Mopar guy, but with the T350, i've heard of people using the stock corvette mechanical governor with great results. Might also look into a transgo kit, but most of all talk with an experienced performance trans builder.