KEEN4T.EXE hard tedlevel 15and press F10+M to see how much free memory (with purging) is left. Use
KEEN4T.EXE easy tedlevel 18to start the level that needs the least amount of memory. Disabling sound and/or music frees up some memory. When you start the game with tedlevel you need to press Ctrl+Q to quit the game, exiting the usual way will hang the system.
The Tandy music uses code that's very similar to the Adlib music code, so I don't think that causes "hitching". Does it only happen when Tandy music is played?