You could watch some other Gundam series. I think Gundam 00 is very good, and the dub is well done. I watched a few episodes subbed a while back, but I can't recall what it sounded like. G Gundam isn't bad either, just has incredibly outlandish dialogue sometimes.
Dialog isn't the only thing that's outlandish about G Gundam. I'd say it's basically Dragon Ball except with giant robots, but I don't recall anyone ever taking a full episode just to power up, so I don't think the comparison fits. The series also has a fair amount of shouting, though its more of the hot blooded and manly sort rather than the screaming kids sort.
As far as Gundam 00, I can't speak for the English dub, but I recall the original Japanese voices were pretty good in that area.
If characters with high-pitched voices bother you, though, a lot of anime may post a problem since many series have underaged protagonists, though it also depends on how under aged they are. Of course, it also depends somewhat on whether you watch your series with dubs or subtitles. In general, I tend to favor the latter as many dubs I've heard aren't very well done. You could try Big O, the voice acting seems to be much more subdued than series focusing on younger characters and there isn't much high pitched screaming at all.
Anyway, in completely unrelated news, looks like I'll finally have something to look forward to!
That's good news, I wonder if it's going to cover just the same storyline as the old anime though or if it will actually catch up to where the manga is.