If I can, I'll make a couple of other suggestions. CLEAN, CLEAN, CLEAN!! Then when you think you have everything spotless, clean it again! The tinest piece of lint from your shop rag can hang a valve. A clean re-assembly on an automatic transmission is critical!
There is another good alternative to the assembly lube LincolnTech38 suggests. Use Vasoline. I've used it for many, many years on the trannies I've rebuilt and it's been flawless. It holds and lubes things well and dissolves the instant heat and pressure hit it. (remember...it's PETROLEUM jelly) I use it for everything I assemble where the lube has to dissolve immediately. Good stuff!