Picked up our PUP from the dealer for minor maintenance and stopped at a CAT Scale on the way home. I was a bit unprepared, and decided to download the Weigh My Trailer app while in line. While doing that, several trucks pulled in line behind me. In my rush, I panicked a bit and didn't get my 3 axles onto separate scales (evidently). I didn't want to hold up the guys who need the scales for their jobs. We 2580 on the steer axle, 5800 on the drive axle, and 380 on the trailer axle which tells me I probably had the trailer wheels mainly or entirely on the middle scale with my truck's rear axle. This is a heavy, highwall PUP with 3800 lb. GVWR. The Colorado handles it very well, so I think I have a measurement error and am not that overloaded on my rear axle. After I left, I recalled some saying that with PUPs the CAT weighing process is a 2-step process, first the truck without the trailer on a scale and then second with the truck pulled forward and just the trailer (trailer's axle) on a scale. Can someone guide me?