I am not an expert, but I have had fruit trees .... Did you prune the roots a little before transplanting? Did you fertilize?
I think it's most likely root shock due to transplanting or it could be due to infestation or other problem. It could also be that the trees/plants you select may not be suitable for your zone..of course, it depends on where you live. You live in TX, right?...I don't know about the particular peach tree you have, but some plants need more mild weather.
Yes, make sure the root ball is beneath the soil surface because exposing the roots makes them more susceptible and mulch with bark or something to retain moisture. Are your trees getting enough sunlight? Trees need sun and room to grow. If they are full sized plants you really shouldn't plant within 15 feet of your house because of root growth.
Water and use fertilizer to give them a good start.
Hope this helps...