We can thank Elon for these great advancements with the gigapress producing huge aluminum parts in place of 100s of small parts that had to be assembled The big three are so far behind Tesla with this type of thinking.
Your truck as delivered including the weight of a full tank of gas creates the payload number. Every truck is a different payload depending on options. The trailer tongue weight is usually the biggest factor for weight, a #6000 trailer could create up to #900 pounds of tongue weight.
I never received said letter either. I am still way behind on updates 'Sept 22", getting one a week lately, but I dont really care anymore. My truck was shutting down systems mostly due to the weak battery and APIM which they replaced both so now it runs pretty good.
I see those things flapping everyday under trucks and laugh. I removed it at the first oil change and in the trash it went. It was wet and heavy, the exhaust weep hole drains on it and had a soft spot. I asked a tech at the dealer and he said its sound proofing, I hear no difference without.