Your best bet is to get the seller to email you a picture of the door data tag and the engine tag. The door tag will give you the build date. Anything built after 01/01/04 is probably a HO. The engine tag will confirm this with the 305/555 or 325/600 output. Finally, if the truck has a CAT, it's defintely a 2004. 5 (325/600).
I'd definitely invest in getting CARFAX with unlimited checks for a month if you are close to buying. The last time I bought a vehicle I found that several that I had been considering had previous accidents with frame damage. Without CARFAX I would have never known.
Also, here is a VIN decoder from this post... .....
https://www.turbodieselregister.com/forums/showthread.php?t=142677&highlight=VIN+decoder
POSITION INTERPRETATION CODE = DESCRIPTION
1 Country of Origin 1 = Manufactured By DaimlerChrysler Corporation
... ... ... ... ... ... ... ..... 3 = Manufactured By DaimlerChrysler De Mexico
2 Make D = Dodge
3 Vehicle Type 2 = Incomplete with Side Airbag
... ... ... ... ... ... ... 3 = Truck with Side Airbag
... ... ... ... ... ... ... 6 = Incomplete Less Side Airbag
... ... ... ... ... ... ... 7 = Truck Less Side Airbag
4 Gross Vehicle Weight Rating G = 5,001-6000 lbs.
... ... ... ... ... ... ... ... ... ... ... ... ... . H = 6,001-7,000 lbs.
... ... ... ... ... ... ... ... ... ... ... ... ... . J = 7,001-8,000 lbs.
... ... ... ... ... ... ... ... ... ... ... ... ... . K = 8,001-9,000 lbs.
... ... ... ... ... ... ... ... ... ... ... ... ... . L = 9,001-10,000 lbs.
... ... ... ... ... ... ... ... ... ... ... ... ... . M = 10,001-14,000 lbs.
... ... ... ... ... ... ... ... ... ... ... ... ... . W = Buses/Incomplete Vehicles with Hydraulic Brakes
5 Vehicle Line A = Ram Pickup 4X2
... ... ... ... ... ... . U = Ram Pickup 4X4
... ... ... ... ... ... . N = Ram Pickup 4X2 DX Family
6 Series 1 = 1500
... ... ... ... 2 = 2500
... ... ... ... 3 = 3500 Less Dual Rear Wheels
... ... ... ... 4 = 3500 With Dual Rear Wheels
... ... ... ... 5 = 4000 DX Family
7 Body Style 6 = Conventional Cab/Cab Chassis
... ... ... ... ... ... 8 = Quad Cab Full Rear Doors
8 Engine K = 3. 7L 6 cyl. MPI Gasoline
... ... ... ... N = 4. 7L 8 cyl. MPI Gasoline
... ... ... ... D = 5. 7L 8 cyl. SMPI Gasoline
... ... ... ... 6 = 5. 9L 6 cyl. Turbo Diesel 24v
... ... ... ... C = 5. 9L 6 cyl. Turbo Diesel High Output
9 Check Digit 0 through 9 or X
10 Model Year 4 = 2004
11 Plant Location S = Dodge City
... ... ... ... ... ... ... ... G = Saltillo
... ... ... ... ... ... ... ... J = St. Louis (North)
12 thru 17 Vehicle Build Sequence
Attention: TDR Forum Junkies 
