Hi Jim,
The first thing to determine is if the html version gets dropped, or if the email client is just showing you the text version.
I assume you remove all the tags before creating the text version?
So a test I'd run is send a mail to a mailbox, and then use NetDemo GetEmial procedure to read it. In that way you can inspect the "Raw" contents of the HTML part, and the text part and see what's what.
Remember it's very common for email readers to default to the text part rather than the html part - so even if both parts are there you may see the text one.
Also, the engine used by email readers to display the html is very "primitive" there's no CSS or JS there. So checking out the "raw" html part may give you some clues as to why it doesn't get applied.
cheers
Bruce