100K points

Two years ago, my son-in-law bought me a 2005 Astro from a Forest Service auction to replace my 2000 after the engine blew. Great vehicle, well maintained. Just went over 100K and I'm wondering what I should do beyond the checklist in the owner's manual. We're thinking about towing a travel trailer (it has the towing package) in the near future, so I'm wondering about changing the timing belt?chain to tighten things up, or does it come under "if it ain't broke, don't fix it"?

The timing chain (not belt) no longer rides on nylon sprocket teeth on the camshaft. Modern North American V-engine timing chain installations commonly last well over 250,000 miles with proper lubrication. Those with automatic tensioning systems tend to have issues at random times, but your straight-up chain arrangement is among the LAST of things which would concern me.

Change the AutoTrak fluid in the transfer case. Search the board archives and rest of the interwebs if you want to know why.

Change oil in both differential housings. If you do only one, change at least the rear, since the Astro is a priority-rear AWD system. That should be in the factory manual.

Inspect the idler arms (both of them). If you've already had an Astro you'll already know why.

100,000 miles is also time for a cooling system flush (not just drain) and refill. That should also be in the factory manual.

Clean all the body rubbers - Door seals, window sweeps, and weatherstrips. Then apply a layer of silicone dielectric grease to all of them by simply wiping it on. The silicone is not a petroleum based product and will not destroy the rubber. In fact, the rubber loves it because it replaces some of the lost oils in the rubber compounds and keeps them from dry-rotting. My 1986 Pontiac still has original weather seals, and even the T-tops are water and air tight with no rot anywhere.

Perform a full body lubrication. Clean and relubricate all hinges, latches, and cables you can access. White lithium grease is the factory treatment because it doesn't stain, clings well, and doesn't damage plastic and rubber.

I could write forever, but the factory manual has full descriptions of service required at the proper intervals. The owner's manual has some general information, but the factory service manual is fairly comprehensive.

Thanks Bow-Tie. In past years, the user manuals weren't as specific. I tried to find something from Chiltons and Haynes with my last Astro, but they both covered all twenty years and weren't very specific, even between the two generations. Can you recommend a good Astro/Safari manual,
besides the $130+ GM manual?