The best time to check an engine is after it has sat for a while. All of the oil drains down into the sump, and this can take some time. If you have a bypass filter, they take quite a while to drain. They typically hold a quart of oil, but some hold two quarts.
The safest way to check would be to drain the oil, fill with the correct amount (5 quarts for a 235 plus the amount for your bypass filter if you have one), then check the dipstick to see where it reads. You can check it both hot and cold to know how it should read with the correct amount of oil in the engine. If you have a bypass filter, the factory marks on the dipstick are not accurate because they do not account for the extra oil needed for the filter canister. Etch a mark showing full with the correct amount of oil so that you have it for a reference.
My hunch is that you are low on oil because of a bypass filter. If your dipstick reads full after the truck has sat for a while, you are at least a quart light. When you fire up the engine, the oil pump will fill the bypass canister and you will not have enough oil in the sump.
Matt
