ALright really need more details, but Ill throw some opinions out there.
Im not going to give you a preference just some feedback and pros cons
SM465
Pro: Quite possibly the toughest tranny ever put in a stock 1/2 ton pick up. If you are breaking these, well you need help
Cons: Limited gear selection, and the draw backs of a stick
Use if: You want the ultimate in reliability and dont mind sawing gears. The stick action is not to be down played, dont try to see it as macho, when off camber and near verticle there are easier things then holding clutch in, braking and feathering a throttle
TH400:
Pro: Without a doubt the strongest stock AUTO ever placed in a 1/2 ton pick up. Darn near bullet proof stock, and can be upgraded to make even better. No stick to mess with
Con: Only real con is no OD makes highway RPMs high. Fairly expensive because of demand, but you get what you pay for, and deals canbe found if you keep your eyes open.
Use if: You DEF. want an auto. Dependability and trail use is #1, if trail only no 2nd thoughts as far as auto are concerned
700r4
Pro: Overdrive allows liveable highway RPMs even with deep rear gears. Plus has lower 1st than any th350 or th400. Can be built very dependable. No stick to fool with.
Cons: Not as strong in stock form as th400. Not everyone knows how to build. Heavier than th400. HATES heat, deep pans an coolers are a MUST.
use if: you have mild lift & tires (<36s). Regular street driving is in your plans. you are illing to spend money to build.
I run a 700, despite having multiple 465s and th400s in my yard. I like it, but I spent $450 in parts to upgrade