77C20 HD with the gold trim.  I don't know what the RPO is for the gold trim.  These are all the RPO codes listed on the sticker.
Even though the RPOs didn't show it this truck came with a 14FF with the big brakes and 3.73 gears.

DG4	Mirrors, the semi-truck kind
F58	Heavy duty front anti-sway bar
F60	Heavy duty front springs--we're talking some monster coils
G50	Heavy duty rear springs
K30	Mechanical cruise control
M40	THM-350
N41	Variable ratio power steering
XUD	245x75r16 tires, at the time they were 30.9.50x16 bias plys
ZY4	Deluxed two tone color
25W	Blue vinly interior
A01	All windows tinted
E63	Fleetside box
G80	For this truck it turned out to be a Gov-Lock
LS9	350 V8 4bbl no smog, no EGR, 175hp
N33	Tilt steering
V43	Painted stamped-steel rear step bumper
YUD	245x75r16 tires, at the time they were 30.9.50x16 bias plys
Z53	Plain gauges, in this case it was a voltmeter, mechanical oil pressure, electric water temperature, and a brake light instead of a clock
25L	Two tone paint.  It came with blue paint (GM Mariner Blue #25) and a white stripe down the side (GM White #12).