Is it smart or safe for differential, for a truck to ride on tires with different tread?
I.e-
one tire is almost new, 85ish
Two are about 65%
And the last is 40ish

 

As long as they are the same size tire, the amount of tread won't put too much stress on the diffs.

 

They are all the same size, 33x12.50r15
Just tread is a mix range from 90% as low as 40%.
The one with the most and least tread won't be an issue?

 

Put the lower treads on the front and the best on the rear. Since they're probably mudders, with big lugs, that can make a bit of a difference, but nothing drastic that will eat the diff.

 

you might just notice it pull to one direction.

 

Wouldn't that slowly run my alignment out of line? Even if I put the better and worst treaded tires on the back.

 

Pull comes from uneven tire wear (in this instance). Either between the two steering tires, or, simply on one tire. Alignment is purely mechanical. If you get a pull, that will give you accelerated tire wear, but, won't hurt your alignment.

 

So all tires, or only the one with more tread will wear faster?