Do not buy any gear at the start of the game! As you pick up your gear at the armory. That will stop the not being about to get aks or vsk's. (This is a known bug thats never been fixed in the game).
Also there is no option to stop overheating in Metro 2033.
Also I have checked the shotguns straight through to the auto shotgun cannon and they all reload fine. Also work fine with Unlimited ammo and no reload.
Plus in my third run I have not come across any unkillable creatures.
Note I am using the 1. METRO 2033 MEGA TRAINER (PATCH #2) on steam.
I suggest to turn of your anti virus and any other av protection you have off. As these can interfere with the trainers functions.