I had the same problem, it turned out to be a bad Perrin EBCS. The heat shouldn't make a difference because SS puts in different wastegate duty cycles based on temperature......so if it gets extremely hot then the turbo ahould just work harder to make more boost. are you running stock tmic or SRI? My car makes 20psi now at any temp, it just spools a little quicker and hits a little harder during cooler weather.