Hi Jerry ... detuning a whole step down can be a bit rough on the guitar. By detuning, you slacken the tension on the strings and they tend to feel much looser and flappier. Here are a few things to try:

1) Use a tuner. Start with the low string, and detune a whole step. Move up each string and repeat. Once you’ve detuned all strings, ending with the high string - go back and repeat the process, starting at the low string again. You might have to repeat the process a few times before each string stabilizes to a whole step down tuning.

2) Use thicker strings. The easiest way to make the guitar more stable when detuning a whole step is to use higher gage strings. For example, if you regularly use 10-46 for standard tuning, you might want to try 11-49 or even 12-52. Using thicker strings compensate for the slacked tension from detuning a whole step.

Hope these tips help. Let me know how it goes!
Mike