1995 Saturn SL1 '95 Saturn SL1 stutters while accelerating

This problem happened suddenly, while driving up a hill. Very jerky acceleration. Jerky accelerating through all gears. No jerking while idling. No check engine light. Saturn replaced the engine control module and wiring. Didn't fix it. Saturn suggests it's something deep in the engine, perhaps related to a leaky gasket (which we know we do have). But in my opinion, the suddeness of this problem cannot relate to the slow leak we have. Saturn "says" they checked the EGR valve and the coolant temperature sensor, and they were ok. However, we've had the EGR valve go before, and the symptoms seem pretty similar. They claim all the injection system is fine. On a trip from Denver to Taos in January we had stretches where we got 48 mpg, so we'd hate to lose the car. Any ideas?
Thanks!