Why aren't customers seeing the $4 First Class shipping option at checkout?

Hello, I want to offer my customers First Class and Priority USPS shipping. Both are set up in my shipping rates. My understanding is that priority is ~$8.5 before discounts anywhere through USPS and they provide a tracking number and the package. First class is cheaper but you have to pack it yourself which is fine since envelopes are no more than $.25 on Amazon. However, when I test ordered my product I was only given $7-9 shipping rates during checkout which makes sense for priority but not for first class. When I went to print my shipping label, I see the first class option which is under $4 and what I would expect. Why are my customers not given the $4 option in checkout? Isn’t first class just going to require me to print the label for 3.97 and slap it on my own envelope? There is a BIG difference between $8 and $4 shipping for most people.

Also, where can I change the “Free Shipping” verbiage that is displayed before a address is entered?

Also, I added USPS first class package service and still no option in the checkout.

That is in your themes translations ( locales) in ‘checkout & system’ category

https://shopify.com/admin/themes/{{_**themeid**_}}/language?category=checkout+%26+system&query=free+ship

where themeid is your current theme id

Where is that in the UI?

https://help.shopify.com/en/manual/online-store/os/using-themes/change-the-layout/change-wording