what else can I check on my 4.3 engine that runs rough at low speed runs fine and faster speed

1991 gmc sonoma sle 4.3 4x4 runs rough at low speed runs fine and faster speed, I've replaced plugs wires cap rotor, air filter set the timing, cleaned venture carbon with cleaner and tooth brush also replaced Idle Control Valve. I've checked all the vacuum hoses and did the throttle body gasket check thing with carburetor cleaner...not sure what else to do... can you help...
Thanks...
Ugo