Nikon N90s twin DS125's

I have Nikon N90s with Twin DS-125. On TTL I am getting slight overexposure. Is this function of strobes and/or N90s?

I can work around with ex compensation but can it be rectified?

Using slides.

Can you dial in exposure compensation for say -1 stop? On my Canon I usually shoot with -.5 to -1.5 exposure for the strobes, as I'd rather have my subject slightly under exposed than blown out highlights...I can fix the rest in RAW processing. I'm not familiar with Nikon, but I would believe they'd have something similar.