Excelente, gracias.

I don't think we can say that Ж is pronounced as Ш at the end of a word after a vowel.

It's rather a middle sound between Ж and Ш.

For example: страж (un guardián) and страшный (terrible), муж (un marido) and мушка (punto de mira) are pronounced different ways - Ж is pronounced softly but not exactly like Ш. But in such words as кружка (кружка пива - un jarro de cerveza) and клюшка (un cayado) Ж sounds almost like Ш.

I can't say exactly, but i think.it's just weak sonorous position for Ж, and it's needs to see, what sound follow it in the next word.

Exelente, gracias.

Toda sonora en posicion final absoluta, se pronuncia como su pareja sorda (sorda - sonora: с - з; т - д; п - б; к - г; Ш - Ж; ф - в):

б --> п: лоб se pronuncia [lop]

д --> т: сад se pronuncia [sat]

ж --> ш: уж se pronuncia [ush] etc

NOTA: En cuanto se pospone una vocal, la consonante se sonoriza nuevamente: сады [sady].