slow trap

iTrader: (22)

my friend is having problems with an avalanche with the 5.3 he just got and we need help. it holds between 30-40 psi while driving, around 20 @ idle which is fine but sometimes it drops atleast 10 psi and starts rattling to beat hell, obviously from the loss of pressure and continues untill you shut it off.

here is where we are bumfuzzled. if you let it sit for a few minutes and start it back up the pressure goes back to normal and all is fine. sometimes it goes for a few days before it does it again. any ideas ?

thanks,mark
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