My ‘19 lariat with 502 but otherwise the same came with yellow sticker of 1625 I took off the side steps for the bed and gained 65 more lbs.

I use every pound when tow my tt.

Wow. Side steps costs that much in weight? I'm not taking mine off but I didn't think they'd be that much of a penalty.

Yup. Payload goes away real fast without even hauling much. My XL has a GVWR of 7050# and a payload rating of 1930#, so theoretical truck weight as leaving the factory of 5120#. However, when I get an actual weight with a my fat ass, full tank of gas, underseat storage, Leer cap, bed mat, and the Husky Centerline hitch installed, my truck weight is 5680# on the scale, leaving a payload of 1370#.

The above text is Gospel! I went with a Soft topper (35 lbs) because I ate up Payload so quickly. One other thing I noticed, is these trucks are so light that you basically want to be fully loaded for a good towing experience, although I did add shocks and air springs to fine tune the towing experience ( I use a spring bar WDH with no sway control, fortunately my trailer works very well at 13% hitch weight.)

X2!!! They do tow very well loaded right at the GVWR +/- 50 lbs.

I have just purchased a 2019 SuperCab 2.7 with 3.55s. I had hoped the payload was the 1640 lb in the brochure but with options like 36 g tank its 1410lb.
I had to buy sight unseen and I know thats my bad but I did have an aquaintance drive it and look underneath and buy since its a 1 owner, clean carfax with 25k mi, I gambled.
I have a 1 ton for real work and towing this is just a groc getter and adventure mobile.
I had hoped to have a payload of around 1700 and augment for the topper and gear with load range E tires and air bags. Realizing that it is still the 8.7 " rear axle.

I know what the sticker says BUT what would could payload be increased to with some mods....???

Thanks in advance

Zero. You can't increase payload.

Actually removing factory options (removing steps, tailgate, etc.) will in in fact increase payload. You can't increase the GVWR without significant cost to a certified up-fitter.

Payload is GVWR - Curb weight as it left the factory with a full tank of gas.
Payload after purchase is GVWR - scaled curb weight of truck.

add items to the truck, payload goes down
remove items from the truck payload goes up.