I have an RT-MOD helmet and actually took the fans out. Made it easier to hear what was going on around me. I did replace the lens in mine and left some small gaps so that air can escape a little so that probably helps.
My armor is ATA and I can do stairs with little difficulty. I know other members have trouble with them. Like was mentioned above you may just need to adjust the fit a little. If I have my thighs too high even walking is a little cumbersome.
Pictures would be very helpful.