Stalling when hot

[newkid87GN]

I hope someone out there can help,,my 87 GN runs great when cold but after driving around for an hour or so the idle becomes very unstable and if you let off the gas rapidly the car will just stall,,it wont even stumble it just stalls and will start right back up,,if I hold the idle up while coming to a stop its ok,,but also runs rougher than usual,,,02 readings at idle when running good are about 850-900,,when running poorly only about 600 and fluctuate like crazy..No codes, new IAC ,changed MAF same problem.. I tried wiggling all connectors and tapping on ECM and no change,,normal fuel pressure readings,,runs great off idle and at wot.could I have a bad ECM or prom? All grounds and other connections look ok..

te-60,,23 row slic,,60# inj,,smc alky,,walbro 255 lph fuel pump,,stock type MAF,adjustable fpr. comp high energy cam,TT alky chip,,