1995 GMC Jimmy 95 Jimmy rough idle

I recently bought a 95 jimmy, 4 door, 4x4, automatic, 4.3ltr v6 engine code W. Its high mileage(300000+ kms). And i'm having a problem with it idleing rough when I am driving it and come to a stop. It runs good when i'm driving it until I come to a red light or stop sign, the tach will jump around from 300 to 1000 rpms and will the truck will stall on me, it always starts back up with a little pressing on the gas pedal, and I can usually stop it from stalling out if I slip it into neutral before it stalls. Since i've gotten this truck I have put new cap, rotor, plugs, plug wires, coil, did oil change, taken egr valve off and cleaned it, put new TPS sensor on it, new fuel filter, air filter, i've done a fuel pressure test and it was all good ( steady fuel pressure, even while driving and stalling out), oh and I had to have a muffler put on it to pass the saftey inspection. I'm pretty good with working on cars, but this rough idleing of mine has got me stumped and I don't know where to look next, any help would be greatly appreciated, thanks in advance.