My vehicle is a 2010 Yukon XL Denali with 129k miles. I think I'm the first one to tow with it, but we bought it used from a street lot, so don't know anything about its history. The hitch looked new when we first hooked up our 5000 lb. travel trailer. It's only been towed 3 times. I'm on a long trip now, 550mi. away from home (no trailer on this one) but I noticed the transmission sort of stumbles when the engine first applies a load to it. For instance, I can be coasting downhill without pressure on the accelerator, at say 55mph. The tach would read 1300rpm's. When at the bottom, I first begin to apply pressure, the engine will rev to 1450-1500, and then lightly stumble until it fully engages, and the tach drops back to ~1350 or 1400. It happens on every occasion that the accelerator is applied; from stops, around corners, etc. I just noticed this happening, so it may have been all along, and I haven't paid any attention. We have a long trip ~1400 miles, of pulling the trailer, so I wanted to know whether the transmission is good to the task, or if I should have it looked at immediately. Thoughts? Thanks.