jsut curious what you all know about the chevy 5.3 vortec is it a decent engine it is in a 99 silverado I am looking at it has 97 on it and I am told mostly highway miles

I know it'* one helluva durable motor. Like our 3800'* it too suffers from intake gaskets and they should be done around 100K.

I've got an 00 silverado and that baby has gone through some stuff... enough that I bent the driveshaft w/o going over something..

Overall, they are a very good engine. They had very little common problems. For the volume of the trucks on the road with this engine, I would say it is one of the least problematic engines out there. There are things to go wrong though, nothing is trouble free.

Some things to look for are:
Leaky fuel pressure regulators (super easy to replace yourself)
Leaky exhaust manifold gaskets/cracked exhaust manifolds (you can hear this on a cold start)
Leaky passenger side head gasket (external leak which is visible from under the hood at the front top corner of the gasket (somewhat expensive repair but not real common)
Leaky intake gaskets (they only leak air, not coolant. This will set a check engine light when they leak)
Water pump (this is to be expected from any engine eventually)

Again, for the volume out there, they really don't seem to have a high failure rate with any of these items.

Hope this helps.

is there much aftermarket like heads and intakes or even a supercharger for it .

All of the above. But I wouldn't */C it unless you did some trans work. My buddy has a 2000 w/ 165K on it. Engine is good, has a minor exaust leak, but the trans is rough on the 1-2 shift and these folks BABY their vehicles. I'd say get a 4L80-E HD from a Denali before putting FI on that motor.

Hmmm Odd you say that Fantastic... I'm anything but gentle on it

Pulled a fork lift outta the grass (HD model)
Cruised a yard of rock down the road at 80mph (truck is a 1/2 ton and a yard of rock is 3500lbs ...I didn't know that at the time)
Pulled a trailer of 8 pinball machines across the cowpath express of PA at 95mph

Trans feels good... not that I'd blame it for dropping any day now...

It is a good motor for sure. Should be lots of aftermarket for it too. I know there was a rash of trans problems in Silvarados, I can't remember exactly what the year range was though. I had a friend in college with one and was on his 3rd trans by 76,000 miles and he babied the truck (for some reason I think it was a 1996). Of course there will always be a lemon for any line of vehicle, he may have gotten it. I do remember him saying it was a common issue with the specific trans he had though. The body style changed in 99 right? So 98 may be the end year of the trans issue? I do not know for sure. Might be something to check on a silvarado forum. Could try www.fullsizechevy.com