Recently I've noticed that when I shift (stick-shift E36 319i), the RPMs are much higher than before, and the speed at the time of shifting is lower. For example, I shift 2 -> 3 at 4000 rpm, and my speed is only 35 mph. Same about 3 -> 4 at 4000 rpm, at a speed of 45 mph. Is my clutch going bad? I don't smell anything though. I remember I used to shift 2 -> 3 at 4000rpm, having 40-45mph on the speedometer

. Are there any other factors that would affect this (apart from rim size and terrain)?
If it's a clutch - how much should I expect to pay to replace it (labor + part)?