97 Mazda B2300 Sputters on acceleration

I drive a Mazda B2300, over 160,000 miles, When accelerated it sputters and the RPMs drop about 500, while idling it sputters to a lesser extent. I've replaced the fuel filter, the fuel pump, the sparks and plugs, the pcv valve, the ecg valve, the water pump, and I tried sealing the gasket heads assuming they may have been cracked. I Don't know what else to do.