94 Prizm Clutch/Trans. Problem?

I'm having an issue with my 94 prizm lsi 1.6L manual trans. 166000 miles. I've begun to notice that when going uphill, if I push on the gas more than a little, the rpms go up more than the car is accelerating. It does not slip out of gear and there is no noticeable noise from the transmission. It just takes a few seconds for the speed to catch up with the rpms. I don't think this is normal. I've had other vehicles with manual trans. and never noticed this. Also I've have this car for 5 years and just recently this started occurring. Any help greatly appreciated. thanks
Chris