400,000+ mile 2011 silverado 1500 maintenance advice

I bought it at 100,000 (engine 5.3) and im going to have to do a LOT of traveling for work coming up. Original engine (I shut off the afm when I got the truck), use bg 44k, moa, and epr on every oil change, (44k with 20 gallons, burned through it before the oil change). Fuel pump was changed out around 250,000. Transmission was new at 150,000 and rebuild around 330,000 (with new transfer case). Front dif was just changed, back dif will be with the next oil change. Control arms, shocks, suspension still looks good. (Control arms and such have been replaced a few times). Normal brake changes also. A few year old battery. It does burn through some oil, but I check and refill it when it needs it. Coolant goes down only in the winter (generally in the summer its pretty good). I do actually like my vechicle, so I really would like to continue using it. I know its still winter, but when it hit 60 degrees, my temperature gauge did rise up a little when I was at a stop sign and hear my fans kick in a little bit, as soon as I drove again, it went back to normal (temperature might of went to 220 and then back to normal temp and fan speed). I put more coolant in (it wasn't low, but I filled it to the top when the engine was cooled off). One of the return coolant heater lines (from the firewall to somewhere, sorry I really dont know what the name of it was actually called) blew off before and had that fixed. Because of the amount of driving I will be doing, I figure I would ask on anything I should replace, especially with the fans kicking in at 60 degrees outside before the summer hits. Original engine and parts, never changed them out. I take it to a reputable local mechanic place that my family had taken there stuff to. They let you know when things actually needs to be replaced or if there still good. I looked online and came up with a few things. Serpentine belt, water pump, thermostat, and maybe a belt tensioner? The Serpentine belt still looks good (no cracks or anything like that). So with the fans starting to kick in a lil bit at 60 degrees and with summer coming up, what parts should I consider replacing and anything else that people can recommend. I also take it easy on my truck, gently bring it up to speed (not grandma slow, but not flooring it either). I put it on cruise control on the high way (65 mph, less wear and tear, unless its in a big city then speed limit) and most of my miles are highway. Any suggestions on things I should replaced? I'll be working around 8.5 hours away from home and figure its best to get things changed or fixed before doing all this driving, thanks for any advice.