Back in 2001 GM had a reflash for some small problems like cruise control down shifting to easy , engine codes caused by the block heater and a warm start and over boost codes. if your truck has this update done you poss have a differnt problem. Do you know how high the boost gets on your truck , my 2001 with a 4" full exhaust and a drop in aircleaner with my hot juice set on level 4 would easy hit 32~34 lbs of boost. Never once did it set a overboost code and it spent most of its time at 0-1000' above sealevel ( some time I would tow into the mountains that crested right around 3500'. If you dont have a boost gauge that is accurate to 40 lbs its hard to say where to start but I would look very close at the wastegate first.
93 c-2500 6.5td,96 6.5td x cab,01 GMC lb7 Xcab ,2004 lly crew cab ,2006 lbz crew cab,honda CBR1100xx,2003 polaris prox 700 , 2001 31' holiday rambler 10K lbs house on wheels!