3000lb slide in with 1000 pound trailer hitched to a 99 reg cab long bed. Was about 1000 pounds over GVWR. 5.3l wit 4 speed auto and 3.73 gears. I never worried about power, stopping was the issue. 5.3l will twist 3 to 4000rpms all day. Got 10mpg with that set up and was running strong at 211000 miles.
Read the owners manual and stay under GVWR and GCVWR and you will be happy. If you want a number I would be comfortable with a max of 6 to 8 thousand pounds behind the Silverado 1500 I had, it was rated to about 8 thousand pounds of trailer. I had a trans temp Guage and a huge trans cooler.
Good luck and enjoy.
