Hy Mr. Giant, I'm no expert and I'm a Canuk to boot but I'll give it a shot, here goes
D = Diesel engine 6-71E
862 = Truck model, four different wheelbases possible depending on whether it is a 1st, 2nd, or 3rd series
S = production year I believe 1958
5357 = regular production number
U = I can find no mention of this letter in this position
As I said I'm no expert, I could be out in left field, but I hope this helps some.