2000 Ford Expedition

I have P0401 egr insufficiant flow. I have changed the egr valve 2 times, I also cleaned the passage out, I am attempting to get a smog test completed. On my scanner it states egr insufficiant flow, but on the computer there states catalyst inc o2 inc, in which I just changed all o2 sensors, all convertors, all spark plugs, & all coil packs, the mafe, pcv system, heavy duty muffler, exhaust pipe and sealed. I do not understand what it could be. The vac. Reg test ok as well. Please help I bought this 4x4 truck aug 2003, drove it the first time 10/31/2003, dec 2003, started my night mare since then 13 rear differentials, 1 front differential, 2 transmissions, 1 shop stole it and damaged the engine by putting a sticky substance in the oil and I had my engine rebuilt. I do not want to give up on it, but I can't pass the smog now.