Having a couple of problems:
Sometimes some Feral Ghouls will be really slow, like walking/running around at 10% of normal speed, really odd.
Also, Glowing Ones seem to be impossibly difficult. They have tremendous amounts of damage. I had ALL companions with me except for Cherry and a single Glowing One can kill most of them off before dying (if it ever dies). They're also ridiculously fast.
Use strong weapons against strong enemies. Mini nukes, heavy weapons, energy weapons.
Vanilla game (even with XFO) have lack of small guns, which can handle such strong creatures.
Also have installed XFO, but MMM is loaded after these. Could this be a problem?
This is normal. Just be sure you use MMM 5 with XFO, MMM6 can be incompatible for now- don't have FOIP support.
I hope you use FOIP patches for MMM and XFO, yes?
http://www.fallout3nexus.com/downloads/file.php?id=4968#fileanchor
BTW, if you using XFO, may be you will be interested in switching to FWE?
1. XFO is old and obsolete
2. FWE based on XFO and have great customusation
3. FWE have weapons from vanilla+ classic fallout weapons + many other mods, even with small guns you will be able to kill almost anything.
If you interested, links are here
http://www.gamesas.com/index.php?/topic/1115446-relz-fwe-fo3-wanderers-edition-44/page__st__120__gopid__16421710entry16421710
http://www.fallout3nexus.com/downloads/file.php?id=2761#fileanchor