auto to manual swap

[Shahnp1]

I mean manual transmission to a automatic transmission

I've been lookn at a lq4 and a 4l80 out of 02 hd silverado and was wondering if i would be better off swapping out my 4.8l 5speed for this setup. how hard would it be change my truck from a manual trans to a automatic??? just wondering what kind of input you guys would have on this. because i know for a fact the junky 5speeds that come in these trucks can't hold up to a lq4, they barely hold up to my 4.8L. So give some feed back on what kind of nightmare i might be getting myself into. thanks in advance