89 s10 blazer 4x4 engine trouble help

Ok my truck is got something wrong with it. Its the 4.3 z motor. It starts fine idles fine runs good cold but as soon as it hits operating temp and I try to drive it it starts hesitating and bogging out. Ive replaced the ECM, temp sensor, temp switch, tps, IAC, VSS, EGR valve, egr vacuum solenoid, map sensor, fuel injectors, check the vacuum which is good, timing is good, no gasket leaks, checked all the wires running to solenoid, new ignition module, , rebuilt the distributer, new cap,rotor plugs and wires, replaced the fuel pump and filter, and stumped 4 mechanics. Funny thing is if I disconnect the vacuum line to the EGR valve it runs great until it throws a code about a half hour after driving it then it starts acting the same way hesitating and bogging but is its at idle its fine and if I floor it its fine. its been 4 months and over a grand and I can't find the problem. PLEASE HELP