blower motor resistors
heads up display dimming
transmission issues
LIM gaskets are common on all 3100,3400,and 3800 motors, but on the NA 3800 the plastic plenum can fail under heat too
also the plastic fuel lines over will time will eventually leak and possibly burn
haynes and chilton cover all the engines but they suck at doing because they made one book for multiple vehicles, either get ALLDATA or GM service manuals