I tow a 6500 lb. trailer with our 2012 XL Denali and used to tow one that was almost identical to yours, so I can offer a few things for you, perhaps.
If your truck has the oil coolers on both ends of the radiator, it will be helpful. The one on the driver's side is for the engine oil and the one on the passenger side is for the transmission. With the HD trailering package, you should also have the additional transmission cooler in front of the radiator and A/C condenser. Pulling across the midwest's rolling hills in the summer with the usual westbound headwind, your coolant temperature will start to climb on the gauge, and your transmission temp will climb with it. The same will be true as you get into the Rockies in either Wyoming or Montana, depending on your route. 2 years ago, I watched an F-150 blow an engine (huge billows of blue/white smoke, not steam) on westbound I-80 outside of Rock Springs pulling a big cargo trailer into a 30 mph headwind, after he passed me like I was standing still. I was taking it easy at 65, in my '07 Denali and had no trouble at all. You'll get there. Your coolant won't boil until 265º and your transmission temp will likely hover around 210-235º depending on the terrain and winds, with peaks as high as 250º after crossing a big pass. Ignore the many charts on the Internet that say you gotta keep the transmission below 175º or it'll blow. Those charts are for 1970's vintage transmissions and fluids. Modern transmissions and Dexron VI fluid can handle much more, so the engineers designed that into our trucks - this directly from a GM powertrain engineer. Trust your truck and the engineers who designed it.
As far as things to do before you go, this would be my list:
- Have all fluids changed (engine, transmission, differentials and transfer case), as swathdiver suggests
- Replace the plastic heater hose coolant tees at the firewall with OEM (not Dorman or any other aftermarket brand). These are a common failure point and yours have aged out if they haven't been replaced.
- Might as well replace all belts and hoses while you have the coolant drained. Check the water pump for leaks, and replace if any seepage at all, with OEM only.
- When you have the belts off, spin the tensioner pulleys by hand to make sure there is no play, and that the bearings roll smoothly. If not, replace both.
- Check your oil and transmission cooler lines for seepage (common), and replace as needed.
- Pay close attention to your oil pressure readings right now. If your gauge shows 20 or below at hot idle, it's time to replace the screen below the oil pressure sender, which sits behind the intake manifold.
- Your motor mounts are likely getting weak. Might be worth having both replaced with mounts for an H3 Hummer V8 (solid, not fluid filled, and way more durable). There are many threads here on which ones to get. If your shop won't use your parts, then make sure they use either the H3 mounts or OEM. Forget aftermarket mounts - they won't last.
- Plugs and wires, if they haven't been done.
- Front sway bar links with better than OEM. This will make a big difference in handling with a trailer.
- If your trailer has "China bomb" tires on it, take it to Discount Tire and have Goodyear Endurance tires installed. You don't want to risk a failure on a single axle trailer.
- Check the date codes on the sidewall of your Tahoe's tires. It's a 4 digit code with the first 2 digits indicating the week of manufacture (01-52) and the 2nd two indicating year. You want your tires to be newer than 5 years old for a trip like that. I see that you also have different brand tires on the front and rear. Make sure you have identical tires on either end of both axles. It's okay to mix/match front to rear, but not side to side. Ideally, I'd want all 4 tires to be identical and new.
- Check your brake pads front and rear.
That's about all I can think of for now. Have a great trip and enjoy the drive!
