My store bought young pepper plants continue dying off....FLORIDA?

I started them in my garden, nade it week 1/2 started to wilt then died. Round 2) same thing but stopped wtering as much, lasted a little longer but same end result. round3) bought new plants, placed them in individual lrg pots with new miracle grow garden soil. I also added MG quick start to help the roots along. the ones i placed in there by just cutting the bottom of the containers are still looking OK, the other ones where i removed the container and placed directly in new soil....yep same thing is happening.I am not overwatering, over fertilizing, they are being kept on the grass so they do not get too hot. I also have been moving them to the shade after about 5hrs of sun. PLS HELP.......Extra info, leaves are not eaten, they wilt, turn yellow, fall off one by one until they are all gone. Some even have gumball size fruits on them when i planted them. Also the root systems look great when i remove them and the roots seems to be growing ok, they dont look or feel wet rotted. Also everything else in my garden is growing amazingly well, tomatos, zucc, squash, carrots, peas, corn...........??????what could it be?