Your profile states a 2003 truck..
The yellow sticker came along well after 2003, if I remember correctly 2010-2011 ish..
Anyway, you can figure out the exact towing capacity very easily.
You need the unladen weight of the vehicle and the GVWR of said vehicle.
You subtract the unladen weight from the GVWR, the result is your cargo weight.
Now you need to subtract you the driver, passenger(s), fuel and any other gear you put in the vehicle, the result is your leftover available cargo weight.
Your trailer tongue weight becomes your vehicles cargo weight so basically you now have the absolute max TONGUE weight you vehicle can handle..
Now, we know for bumper tow trailers you need to have 10% - 15% of the trailer weight on the tongue..
You can now DIVIDE the leftover cargo weight by .10 (10%) and the result is the max trailer weight you can tow..
Now we know that 10% is minimum tongue weight so we need to give ourselves some room for additional tongue weight so we DIVIDE the left over cargo weight by .15 (15%) and the result is the max trailer weight you can tow at 15%..
Example, say you have 600 lbs of leftover cargo weight.. 600/.10 is 6000 lbs of trailer..
At 15% you can use 600/.15 and the result is 4,000 lbs of trailer..
Keeping in mind that those are the absolute max fully loaded weights, not "dry" weights..