94 K1500 Runs Rough When Cold

I have been chasing a problem in my '94 K1500 w/305 v8 for a couple of years or more. I let it warm up for at least 5 minutes, before leaving each morning. It idles fine, but I wouldn't consider it a "fast" idle. For about 1/2 to 1 mile, it stumbles, during mild acceleration. It tends to clear up more quickly, if I give it more throttle. I've covered all the normal items, such as plugs, wires, cap, rotor, coil, MAP sensor, O2 sensor. I've checked for vacuum leaks, but that doesn't make much sense, considering the truck runs beautifully at all other times. Is there some sort of sensor that controls the butterfly valve? I've searched the internet and my repair manual, but can't find anything. I'm sure this is a simple fix, if I could just find the problem. Any help would be appreciated. Thanks.