EGR causing 4.2L Engine to shake 2000 E150 4.2L V6

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EGR causing 4.2L Engine to shake ?? 2000 E150 4.2L V6 (146,000 Miles) The EGR system starts working when coolant sensor says 115 F then at 1950 to 2050 RPM engine starts to shake like a front loader washing machine!!! In Drive the most in Park a little. Changed the EGR valve, DPFE sensor and EGR control solenoid. Checked voltage to DPFE bottom wire (Ref) 5 vdc but top wire (Sig) fluctuates between 1.05 vdc and 1.8 vdc with different throttle positions. (I thought its suppose to be between 5.0 vdc and 6.0 vdc but that would be impossible with a 5 vdc supply) If I disconnect the vacuum hose to egr valve and plug it or if the coolant temp is below 115 F the van doesn't shake. We checked the EGR tube and vacuum hoses all ok. Secondary butterfly valves open fine at correct RPM. New Spark plugs, wires and coil. Had our mechanic run scanner and tests, not a thing showing. When the DPFE sensor was changed on first startup it threw a 1401 code. But never did it again. No air leaks on egr valve gasket, checked all wiring connections, checked everything but vacuum reserve tank. WE HAVE NO CLUE WHATS WRONG. runs GREAT at Idle. with and without EGR connected. Need help. Thanks