EPA limits a gas pump to 10 gpm, so the gas station pump averages 5-10 gpm.
Average semi pump is 40 gpm and the "satellite pump" receives it's fuel from the same pump/meter in the "main pump". Average truck will get between 75 and 150 gallons per stop. Average truck has two 100 gal tanks. Some carry twin 150's. You don't want to spend 30 minutes at the pump.
With your pickup at the big truck fuel island, the point is to hang onto the handle and don't run it full open. Depending upon your tank size it may only take 15-30 seconds to fill up.
The diesel truck nozzle is the same size as the old "lead nozzles" to support the higher flow rate. The unleaded nozzle (smaller size) is the standard gas nozzle these days and gas stations may use the smaller "unleaded" nozzle on their lower capacity diesel pumps. The pickup manufacture to save money, figuring most people would fill up at the corner gas station, installed the smaller nozzle fill line on your truck. That's just a guess but a standard part for all versions of the pickup makes sense to their bottom line.