Problem with other stations decoding my FT8

I need help getting my FLEX -- 6400 working with FT8.

The symptom is that I appear to be transmitting the sideband signal, bun no one can decode it.

I have set up my radio both manually and with Slice-Master with the same results. I appear to be transmitting a signal and if I listen to it, it has the wavering tones of an FT8 signal.

I am using the latest version of SmartSDR, v3.10.10, and the latest version of wjstx, v2.7.0. Wsjtx will decode FT8 signals while receiving and show delta times in the 0.2 to 0.4 range with some outliers, so I do not think it is a timing issue.

I had a friend who lives several miles away listen to my transmissions. He could see the RF but could not decode the FT8. We tried several different bands with 20W. On my receive cycle, we compared wsjtx decoded FT8 signals for time differences and strength and there were only small differences with many the same.

The only thing I could think of was that somehow I was overloading the audio signal which was causing enough distortion where the FT8 code could not be decoded. The gain on the transmit slice was in the normal range and I even tried adjusting it up and down some with no difference.

I loaded wsjtx on my MacBook Pro and had wstjx on the Mac decode the audio coming from my computer's copy of wsjtx using the builtin microphone on the Mac. During the receive cycle on the computer, it did not decode all the audio signal but it did decode about half - which I considered reasonable for not being directly connected. I compared the signals it did decode with the ones from the computer. The ones it decode matched the ones on my computer with some slight differences in strength and time. During the transmit cycle, it could not decode my FT8 signal.

I have used my computer and same antenna system, off center dipole, with my iCOM IC--746PRO and made a number of contacts on FT8.

Any help would be greatly appreciated,

Jim KG5QFD