I know who to have build your tranny. His name is Kelly Harris, built zachs (starlite diesel) trucks trans. Built mine and smokinu497's as well. 30+ years experience as a gm mechanic, and builds trans as a living now. He uses suncoast parts.
Pm me for his info if you would like, your welcome to use whoever you like but I would highly recommend him.
Mine cost me $4400, GMAX 6, deep pan, 1056 converter and he replaced a u joint for free.
Matt moon and Gillette go to him I believe, or that's who they told my friend to go to (smokinu497) and we have both had great luck!