1989 Other GMC Models idle issues

I have a 1989 gmc v2500 suburban with a 5.7 tbi.
It initially failed the emissions test in mass so I replaced the egr valve. When I brought the truck for a retest it failed again. The Mechanic suggested I replace the oxygen sensor he told me that this usually fixes the problem. I replaced the sensor and the truck ran beutiful for about 4 hours. That same day the truck stopped idleing and began running like it had a choke stuck. So many suggestions and many frustrating days later I still have a poor idleing truck. I have replaced the temp sensor in the intake, The IAC sensor, tps, map sensor, Spark controll box, cap, rotor, wires, plugs, air filter and most vaccum lines. Im running out of patience and money PLEASE HELP ME!