what transmission to use with new hemi 5.7

Don't forget if you get rid of the factory FI, you will then have to run spark control from a different controller. There is a distributor setup out there that was made for the Nascar version of the G3, but its something like $2000 just to be able to run the mechanical distributor. I linked the MSD spark control box for you below.

MSD 6013 Ignition/Timing Control for Late HEMI

If I was doing a G3 Hemi install all over again, I'd run a Megasquirt system. There is a plug and play out there now for the G3 and will allow you to tune at your own leisure as well as run a mechanical throttle body.

MS3 Gold Hemi | MegaSquirt