I just want to see if I'm nuts or something...

I'm running Bitcoin Utopia on a couple crappy ATI cards I have at work. It had been working fine for a while, but lately, it seems like the WUs are falling off the GPU. They'll crunch up to 90-95% really quickly, then the last 5-10% goes at the pace of a snail wading through molasses in January.

Is this normal? Should I be doing something differently? My credit output on this has dropped by around 80%...