I have a 2005 Silverado Ltz ext cab 1500 problem is when I stop or truck sitting it will not blow cold air it has the digital temp control set to 60 which is the lowest setting air blowing out around 75 on warmer days but when driving down the road it's blowing 38 then stop for traffic it's back up to 75 again I have replaced the condenser blew all the a.c. lines out replaced the compressor and accumulator the fans come on when a.c. is turned on have plenty of sweat on the accumulator any help would be appreciated