theres how to's for both if your the diy type guy.

transgo shift kits are about 40 off ebay and work real good. many use it and love it.

the cooler, a 24,000 gvw truck oil cooler works well. iirc tep also sells a kit.

we also got a gxp owners thread here, some of them guys have gone mod crazy on them. cams, heads, intake swaps headers and all that cool stuff. but with all that you'll want a built tranny to hold it all.