Well the 5.3 is LS based and dead nuts reliable. Should have a 4L60E, don't think they went 6 speed yet. Keep the fluid changed and add an aux cooler. Should treat you right.
Might have the G80 rear end. It is okay, they are known to break when not treated properly or you do a lot of towing.
They are easy on oil and have a huge aftermarket since the 5.3 is just a smaller LS1,LS2,LS3 etc etc.
Plenty of LS engines with high mileage out there. How many miles on this on?
They have a dry intake. No oil or coolant touches it. Dex-cool is fine in these. 5W-30 works well. I run 10W-30 in all mine, but I get it cheap and it does not get cold here.
Some have the steering linkage knock. It is more of an annoyance than a hazard. Some still have piston slap on a cold start. Not an issue, however I doubt by 07 you will have it.