So if I understand all this info I've been trying to absorb the order of effectiveness sort of goes..

True Track---> Detroit locker---> Full air locker
Each one having its own advantage but progressively more effective and expensive.
I understand if adding any of these that's the time to change the gears since they will be out anyway. Are the HD axles usually recommended for the TT and Detroit? It's my understanding the weak point in the differential isn't the axles (when it's unlocked) it's in the inner spider correct?

 

http://www.ashcroft-transmissions.co.uk/index.php

 

Wow that's a ton of info. Thanks. I love the old chevy video.

 

I would probably change your arrows a bit.
True Trac < Detroit Locker < or = Selectable Locker(typically air).
A Detroit will provide the same amount of traction as a selectable but it is always on, you can't turn it off. An air locker can be turned On/Off at will, but there are more components involved which basically adds another link in the chain that can fail.
Typical air locker setup consists of: Compressor, Electric toggle switch going to a solenoid which puts air to the locker. The solenoid can fail as can the air line. I replaced my electric switches and solenoids with pneumatic switches to simplify a little, but I have more air line running now. Everything is a trade off.

Adding a locker means the diff will need to be set up again from scratch. So changing the gearing is NO extra work
The weak point on a stock truck is the open diff. You'll chew the spider gears before you break an axle. When you go with a locker you're eliminating the diff as the weak point, so the next weakest link is the axles. It is highly recommended to run HD axles with a locker because breaking a stock axle is much more likely and can have catastrophic effects.