trans. shuddering

when im driving at normal speeds, ocasionally at around 2k RPM my trans. will just start shuddering. it happens for a few seconds and goes away with a tap of the gas or letting off the gas. it happens after the car has warmed up, but not before that. when it happens, RPM remains constant. its very annoying and im worried that it will develop into something worse. 96 civic lx.