What lakngulf means is that many of us around here are organic gardeners who don't much believe in the use of Miracle Grow or especially chemicals like Sevin. We will try to play nice and not gang up on you!
Re the Sevin, I will just give you this link:
In that thread are links to a couple of articles about Sevin. You can read it and see what you think.
Re the MG, I just responded to your post about the bougainvillea you were treating with MG every other week and wondering why it wasn't blooming.
Too much nitrogen will slow down your tomato production too. But as far as existing tomatoes not ripening up, that likely does not have anything to do with the MG or Sevin. First question would be what kind of temps are you having? You are in Fl, it's probably HOT, right? Tomatoes don't ripen very well when the temps get to 90 degrees and up. The lycopene and other substances responsible for ripening break down in that kind of weather.
Some of our TX members say they just give up on getting ripe tomatoes in heat of summer and just take care of the plant so that it makes it to when the weather breaks.