A basic wt with cruise control, just lost 3lbs of payload vs brochure base eight. Factory brake controller may add another 3-5 lbs to base wieght, or a loss of 3-5 lbs of payload. Did you get ANY options at ALL. They may be the approx 100 lbs you are not finding. 4 power windows are 100 lbs. 26-35 lbs per door!
If I may, most trucks I've bought, have been within 20-40 lbs one way or the other from how speced, what they should wieght. Most scales read in 20 lb increments. You'll be off a fraction due to scale round up or down.
Look in glove box, or door frame and see if a camper load or max payload sticker exists. That's a better factory wieght number to work with vs brochure. I've only had ONE truck of a dozen thru the years close to that figure. It was a 2000 c2500 with 2 chargeable options. Auto trans, trim rings, and not chargeable, cloth seats. It wieghed maybe 60 lbs more than base config.
Marty