Transmission Driveline Question

First off Hello!

I have a new to me 07 Silverado Classic WT with the 4.3 and the 5 speed manual. Eventually I am going to swap a 5.3 into the truck, but for now I was wondering if I could do it in stages. For instance I want to goto a automatic tranny. I have searched and it seems that everyone goes from auto to manual and not the other way around.

My question is what trans should I look for should I be looking for a 4L60e or a old school 4L60 or 700R4? I want it to be as plug and play as possible. I am 100% planning on going with a floor shifter, and not interested in the column shift. I would think that the change from manual to auto should be easier, but I just don't know. (I also know I need a 2wd transmission since the 4wd is a different length.)

I want to do the swap in stages to spread out the $ pain. Since I am slightly lifted I want to do a rear gear ratio change too, but that is a little bit down the road. With my current 3.23 it is a little dogish in acceleration.

Any help would be appreciated! :D

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