Is it permitted to speak to Hashem in the shower, or is it not respectful?
It is forbidden to recite berachos or biblical verses in the shower. However, it is permitted to think about Hashem, and it would also be permitted to “speak to Him” in your own words, if you feel that there is some immediate issue that needs speaking out. However, it is not the appropriate place for place for serious prayer.
Sources: See Chochmas Shlomo, no. 85, who writes that it is permitted to think about Hashem in a bathhouse/shower.