I never had those side effects, but recently I started to suspect that Prevacid was causing me some dyspepsia. I stopped, and of course GERD symptoms returned but some of the dyspepsia did go away. Bowl movements are also a little better. I never had diarrhea but I did have loose poop.
For a while, at least, I'm just going to treat the GERD with Maalox and stuff and see how it goes.