All credit to jackfuste at WSGF for this fix
Download and install HxD (it's free) - http://mh-nexus.de/en/hxd/
Start it up and open EDF-IA.exe (location: Steam\steamapps\common\earth defense force insect armageddon).
Scroll down to the line 00024BA0 and change the values "54 24 24" to "D1 8B D1" and save
I did ask him if it was possible to make it run at 120fps but he never got back to me :D
Again, all credit to jackfuste at wsgf for this fix. It's not my work, I just took a look at his replacement file, saw what he had changed and made a note so that it could reapplied when the game was patched.