Salteen, doesn't your truck have an ident plate like this, inside the driver's door jamb?

IMG_2095_door_ident_plate.jpg

Going with what this says should be right, or you can go higher, up to the max shown on the tire sidewalls.
You say you can't find this on your sidewalls, that's surprising, I always see the max load & pressure on every
tire I've had..... (the ram is at least my 30th vehicle I've owned)

Also - the chart you show above shows a dramatic increase (from 30 to 43, etc.) due to going from a 225
tire to a 235. I don't buy it - that's a small change in tire size.