A co-worker of mine pulls a FX23. He had a 2005 Tahoe and said that it pulled ok. He had the 5.3L engine and 3.73 axle with a tow package on it. He recently traded that Tahoe in for a 2006 ext cab chevy 1500. This truck has the same 5.3L engine, 3.73 rear end, and tow package on it. He said that it is night and day difference between how the truck pulls it compared to the Tahoe. He never really complained too much about the Tahoe, just said it felt "slightly unstable" at times when he was pulling. He said his new truck pulls it way better.
I think both the FX23 and the 24RBS are almost the exact same weight, so it is very comparable. With his Silverado now, he said he can consitantly get about 11-12 mpg while pulling about 62mph on the interstate. He said he was barely able to get 9 out of his Tahoe doing the same towing.