You would normally turn off the PianoTeq reverb. But experiment--setting different reverb times and lengths using both the internal and an external reverb might create a sound you like. Different frequencies would then decay at different rates. (Try the Ambience reverb vst.) On the other hand, more CPU is going to get taken up.
If you have a good cpu, also try PianoVerb. If you follow the instructions and lower the body resonance an octave, you can get a wide variety of sounds. Listen to the lower bass in PianoTeq with PianoVerb in the chain with PianoVerb lowered an octave. Again, however, the cpu will take a hit. (With less than a 2 ghz system, you may get a freeze-up after hitting a very few notes: lots of computing going on.)
More generally, be sure the sound that you are listening to is the result of reverb--in PianoTeq, the Harp\body resonance and the Full Sustain Resonance (on the Options menu in the lower right corner of the interface) may be contributing to what you take to be reverb.