wierd vaccum problem

[sr20tom]

OK i have 3 boost gauges. Greddy 60mm AEM tru boost and the power FC d-jetro. The D-jetro reads fine cause it runs off a seporate vaccum line. now the other 2 lag behind. The AEM only does it for about a min while the car is cold. and the greddy one is really wierd. It always lags. Ohh it also reads 0 for about 3 mins while the car is cold. Here is the wierd part. I took out the radio where the sensor is, and tried to blow on the sensor by varying the pressure rapidly and the gauge was fine. I plug the sensor to the vaccum line and the gauge is still perfect, then a min later it starts lagging. I repeated the unplugging part a few tmies and it did the same thing. I doubt its a leak cause when i unplug it and plug it back in it responds perfectly for 30sec. I pulled on the line to make sure its not crimpped. I am lost.