EGR failure code

I have a 93 chevy 4 wheel drive pu. Odometer says 250,000 not sure if original miles on engine. I am getting a code 32 egr failure. I have replaced the egr valve the egr solenoid, tried a different used 02 sensor, cleaned the connections on the ecm. Replaced a ground wire from cab to engine block. I am still getting service engine soon light evertime I drive. Any info. On other possible things to check or replace would be greatly appreciated. Thanks, chevypu