Nice, it only tries to stuff a character once a minute, and when the stuffing routine is called, if the computer has been idle for less than a minute, no stuffing occurs. I was thinking the same thing during my earlier troubleshooting (no sense stuffing if they are active and no problem with whatever you stuff if they aren't) but didn't know enough about AHK to do it.
As I mentioned above, with the random char range set to 97,122 the application I desire to keep active still goes to sleep, but if I change the range back to 65,90 it works fine. I have not a clue why this would be, but I took your version 1.2 and tried it, and my application still went idle. Then I made the single change of the random char range to 65,90 and now it works perfect.
If you decide to change the range to 65,90 and post a new version, I noticed that when you compiled 1.2 you didn't include your spiffy exclamation mark logo so the green H logo is used. I extracted the logo out of the previous version and recompiled my own 1.2a with the new char range and the logo.
I think we might just be 100% good-to-go with this.
Thanks again for a great program!