The problem with the roush aluminum intake manifold is it also has the hot water cross over built into the leading edge. What HE are you using ? Cruising in 70-75F summertime heat, IAT's are typ 120 F.... and drop a bunch with gas pedal mashed, blower on. Just cruising, and the air is traveling so slow through the intake manifold, it gets re-heated. Drop down a gear or two, or get into the gas a bit ( blower off)..and now the air travels in + out of the hot al manifold quicker.