[chris71]

a built 700 will cost the most out of the 3, i think you are looking at at least 1000$ for a nice built 700, and if you do the math behind it, unless you drive your truck alot of miles everyday, then most of the time its not even worth it, plus the 700 has the touchy TV cable, that controls shift points and fluid pressure, if you screw that adjustment up you can blow the transmission in a few months.

My vote.......rebuild the 400, its beefier, you dont have to mess with shortening the driveshaft, re-drilling holes in the frame for the 350 position tranny mount, and unless you are drag racing and worried about every tenth of a second, dont worry about a better 1st gear with the 350, i have had several 350's cases crack on me and am sick of them, i am considering a 400 the next go around.