Thanks for ideas....tried them all; no change.
However, if I disabled Use high speed timer in millisecond delays, the problem improved for characters that were dropped in the middle of a word or group of lines. For instance:
"ManagePLUS" was "anageLUS" but after disabling the high speed timer is "anagePLUS" (The "P" is now present.)
This was not a problem in the old Postbox version, and is not a problem in other applications. Likely due to Postbox using a significantly cross-platform code base, which somehow is not fully compatible with the keystroke sending facilities of Windows.
...if you have any other ideas, I'd be glad to hear them. Thank again.