Everything Toyota is a weak spot. That said, you can make parts last forever or you can grenade your entire truck if you're trying to. I feel that this thread has missed a couple important points.
I'm basing this post off of a Toyota running all Toyota drivetrain and 37" tires. Think cookie cutter Toyota trail rig. This is what I've had the most experience with personally, and from watching others.
New birfs are the first step. 37's will pop stock birfs before any other parts most of the time. If you're strapped for cash or don't want to dump too much into a Toyota axle, I've seen 27 spline chromo birfs and stock inners hold up to a lot. Longfield's are great, and come with a warranty. Both the 30 spline set and the 27 spline set are plenty strong. You will not worry about shafts again.
Steering, go high steer with an IFS box. Most do. Stock push-pull will not take abuse, the J-arm will break. I've never seen anybody blow up the FJ80 tie rod ends that come in the package, those will be fine. Not saying it can't happen, it's just not something I worry about. If you add hydro assist or go full hydro, the weak link in your steering will be the knuckle studs. Put ARP's in if you do.
Hubs, the stock Aisin hubs are very strong. The weak link is the hub studs. Stock hub gears, in my experience, will hold up longer than the stock studs will. If you put ARP hub studs in, then I'd put the Longfield hub gears in.
Diffs, gear it if you drive on the street. I haven't been convinced that any ratios are particularly stronger than others. Shock loads kill diffs. If you're on an incline pinning it and hopping around, I'd be most worried about the rear diff. Put a V6 diff in the rear because there is no good reason not to, high pinion in the front if you can.
For lockers, ARB's won't break unless you're engaging and disengaging them while moving quickly, e-lockers have one weak side gear, and Detroits have been known
to break from the shock load of a shaft breaking.
Stock rear shafts are very strong. I've seen a lot more blown up rear diffs than I have seen broken shafts. I wouldn't bother upgrading them. If you break one, spares are cheap and easy to find. I'd say shafts will pop if the tire is very bound up or trying to climb an undercut ledge very slowly.
As far as the drivetrain goes, transfer case output shafts and input shafts are the two common breaks. Rules of thumb here are: 21 spline crawl box + 21 spline rear case = broken rear case input shaft. 21 spline crawl box + 23 spline rear case = broken output shaft. If you put Longfield's chromoly output shaft in the tcase, you move the weak link to the front output. There is a chromo front output available now if you continue to go through tcase breaks. If you're breaking things this far up into your drivetrain, think about ditching Toyota stuff.
The front axle housing itself is a weak link. They are easy to bend. Gusset them. I'm on my third one. If you like to jump your truck or charge through whoops with your solid front axle, that's when the housing will bend and when you should be worried about your trunion bearings and pins. Aftermarket housings are available and stronger than stock.
Only other thing I can think of is Toyota driveshaft u-joints. Toyota made these out of Unobtainium. If you break a stock Toyota driveshaft u-joint, feel proud of yourself. Very rarely do these let go.
