Working - thanks to everyone who replied
Jhpete1, I believe you nailed it. I believe every time before, I had the ac's on, but on low or auto. The temp was very high day before and I'm sure I had the ac's cranking. Regardless, I started the generator, turned the ac's to low, removed shore power and have had no issues. I have done this four or five times now... Just to be sure, I did it with thew ac's on high and BAM, no joy... The transfer switch would not switch...
I wanted to thank every one for their great suggestions and replies. I can see RV ownership is going to be a fun and challenging exercise.