Replace all 7 cooling system hoses.
+1 on the OEM axels. +1 on the CTS.
+1 What everyone else wrote.
More things to be aware of with these-
The shaft that drives the main oil pump in the 3AT should be good for close to 200K miles. IF you get close to that, replace that shaft before it fails. If you want one of those shafts, start looking now.
I've run Amsoil synthetic ATF in the 3ATs since 1988, and have had very few problems with them.
Check that front diff gear lube at least 4 times a year. Running the diff dry causes a lot of problems before the noise gets loud enough to alert you. Mine turn 4000RPM at 65MPH on the highway, not a problem.
#1 thing to maintain is the cooling system. Radiator condition, not corroded, not blocked, etc. These engines do not like to run with air in the cooling system. Well, they run, but when the temp goes over normal due to air, the head gaskets get damaged or outright fail.
The alternator will wear out a brush around 150K miles, like clockwork. And you can only tell if you happen to be idling in the dark with everything off, and notice the alt and a few other red dash lights dimly glowing.
If it develops the click - no crank problem, adding a relay in the starter solenoid circuit is the fix.
Start collecting parts, as many are NLA. Others are order and wait.