I assume you're playing on Quick speed, because it's 200 faith for the first Great Prophet on Standard. If so, the 134 is just the minimum required for a chance to generate a GP. Once you meet that threshold, there is a chance each turn that you generate one. My guess is that you've just been unlucky so far. At +20 fpt, you've only gone a couple turns without getting your GP so far (131 was too soon, 151 and 171 were your first 2 chances).