They are generally pretty reliable if well maintained and treated right. Some areas that have occasional problems -valve lifters, camshaft (if lifters seize) (mainly on 06-12 trucks I think - early years of the multi displacement system), exhaust manifold studs breaking (most years of 5.7 and 6.4), ball joint issues if a previous owner lifted or leveled without putting re-angled arms too. Most issues I have heard of from owners are because of rough usage, low maintenance or putting performance chips, cheap lifts ect...