Easy way to determine how much Travel Trailer I can buy?

You should be fine with a trailer that weighs a little over 6000# dry and 8800# gross. My truck has a similar tow rating to yours. My trailer weights 6250# dry and a little over 7200# camping ready with 1/3 tank of water. I have about 2000# left on my gross combined weight and about 500# of truck payload reserve. Just my wife and I as passengers. Trailer tows fine with my 2016 Sierra 1500. Good hitch is critical.