Plants don't really need soil, they just need the nutrients that are usually found in soil. If you provide water, sun, and nutrients for your plants via fertilizer your plants should grow fine (hence why hydroponic growing works). Also, if you have never had your plants outside then you won't want to just take them out and transplant them all of a sudden. I would try fertilizer first and if that doesn't help you can always transplant. If you intend to transplant right off the bat do a search on "hardening" your plants before putting them outside full time.

Thanks for the followup pepper_tamer. I just put a couple of em outside just for kicks and since I have so many. After cutting away the styrofoam cup, I noticed that the root system was very matted and I am thinking that the plants are simply just outgrowing their pots basically, we'll see how things go over the next couple of days.

Could very well be, although I've definitely grown plants in small pots as an experiment last year they still grow pretty decently. I had some cayennes that got about 1.5 feet tall in a tiny pot that was 3" wide and 3.5" deep. By the end of the summer there were more roots than actual dirt lol. Anyway, I would still look into some fertilizer; leaves definitely start to turn yellow if the plants aren't getting enough nitrogen.

Well, I am in the process of transplanting them into 5" peat pots I picked up last night and I am filling the pots with the miracle gro flowers and vegetable potting soil, lets hope they become happy plants, :).

Well, the 4 pepper plants that I put out seem to be doing fine after 3 days of being out there, so they look like they are going to be doing fine. Our weather doesn't get below 50 at night here in May (Kentucky) so I think they will be fine. I may take the rest of my plants and stick em outside for a half day on one day and then a full day on the next and then plant em, but I think they will be fine.

Oh, by the way, I do believe that I had messed up by not thinning my plants way back and letting them grow too big in my styrofoam cups and not transplanting them into good soil and reusing my remaining seed starter mix. I will know next year, this was my first year to grow peppers, but so far I have not killed any, I think I transplanted them just in time, they seem to be coming back to life, the yellowing is going away and one even seems to be forming a flower, ;)