Temps of 375 to 425 should be no problem. Keep her stoked up. Build a bigger initial Fire and Feed the wood more often to maintain higher temps. Also put fire brick in the bottom of the firebox; under the grate and some days ( when it’s wet and humid) on the top of the firebox as well. It helps channel more of the heat into the cooker. You might also use pizza stones on the racks.
Jim send us some pictures and an email about your results with the Lang BBq Smoker when you can.