changing rear end ratio from 4.11 to 3.23(or close)

[steeeeeve]

Hi fellas,
Need advice. Please explain this to me like i'm a child.
I currently have a 4.11 rear end and i'm looking for better cruising rpms. I will not be doing any burnouts or towing anything heavy.

I'm going to have my mechanic do this job, but I still want some insight.

If i'm going to a 3.?? ratio do I need to have the carrier changed also? And if so which carrier? A type 3? Can someone show me a link or ebay (used would be great $$$) item that would be the correct one? It's pretty confusing. (for me- tired of ordering wrong parts)

Or are there shims? I've read than new 3.9 and lower will work with type 4 carriers.

I don't know if any of this is true.

thanks,
steve