What are your thoughts on how to increase the rpm limit on a 2008 LS3? This is a 6 speed manuel with 3.43 gears. Any suggestions on how to improve torque and hp numbers would be appreciated.

Thank you.

Increase rpm limit? Remove the rev limiter. ;)

Smaller bore/shorter stroke is the general rule for high rev'ing motors. Smaller parts and shorter distances makes for less of the physics that destroy engines.

But you'll be wanting to balance, lighten, and possibly knife-edge your crank; lighten and weight match your connecting rods and pistons; and a lightweight, bulletproof valvetrain. (valves, lifters, pushrods, rockers, springs, etc..)
And a few other things I'm probably missing, but that should have you well on the road to 8K and an emptier bank account. :D ...you'll also be trading a bunch of torque down low for more hp up high.

My suggestion is you keep it where it is for now unless you plan on swapping out your camshaft (since the stock cam is already dropping power before the factory rev limiter kicks in) and then upgrading your valve springs and retainers, in which case you will be able to rev to 7K or more, but engine life will suffer as a result.
Tips for increasing power and torque depend on your goals but I'd get a nice set of long tube headers and a tune for starters; you can make over 400RWHP with just that on those motors, and it will be the foundation for any other mods you do in the future...

My understanding is the RPM limiter on C6's in not simply a matter of unplugging the limiter, but invovles shutting off the fuel supply for a limiting factor. How do you change this?

See reply below regarding fuel supply as the limiting factor in C6's...how can you change the fuel supply to allow higher revs. I am not trying for 7500 plus rpms, but nearer 6500-7000. Considering the internals of this engine this expectation is not beyound the capabilities of the engine. With 3.43 rear gears the engine easily reaches the rmp limit quickly in gears 1-3.

My understanding is the RPM limiter on C6's in not simply a matter of unplugging the limiter, but invovles shutting off the fuel supply for a limiting factor. How do you change this?

There is no limiter "plugged in", it is simply a command cell within the ECU that can be set at whatever number you want (all the way to 8192RPM it seems). The strategy can be ignition cut, fuel cut or throttle but the way it is set is simply by plugging a different number into the cell and reflashing the ECU. Here is what it looks like in HP Tuners, the most popular LS-Engine tuning software (3rd cell down, highlited):
http://i529.photobucket.com/albums/dd339/sampowerlabs/revlimit.jpg
See reply below regarding fuel supply as the limiting factor in C6's...how can you change the fuel supply to allow higher revs. I am not trying for 7500 plus rpms, but nearer 6500-7000. Considering the internals of this engine this expectation is not beyound the capabilities of the engine. With 3.43 rear gears the engine easily reaches the rmp limit quickly in gears 1-3.

I would love to know where you got the idea that 7000RPMs is not "beyound [sic] the capabilities of this engine". You said "Considering the internals". Have you examined your valve springs very carefully and assessed that they will not float at that level? During that consideration, did you consider the impact 7000RPM will have on component longevity?
Let me re-state what I said with an illustration. Here is a bone stock GM LS3 dyno, and the same engine with a reprogrammed ECU:

http://75.180.27.125:50001/Dyno%20Graphs%20and%20Pictures./Dyno%20Graphs/2010%20Camaro%20SS%20LS3%206M.jpg

You will notice that horsepower hits a peak at around 5800RPM (the factory quoted power peak happens at 5900). The engine's efficiency is dropping off fast after that point and even at the factory rev limit you're already down in power. Spinning it past that will only make less and less power, which will not make the car any faster.
Also, while I won't dispute that the engine can probably spin at least close to 7 grand a couple of times, I really hope you realize that it would be a matter of relatively short time before one of the following happens:
1- Broken valvespring
2- Valvespring retainer breaks or comes off
3- Valve float

When that happens the piston will contact one of that valves, and, at that moment, you will instantly realize why the factory rev limit wasn't set at 7 grand. Sadly, that realization will come with a +- 10,000 dollar bill as well, because not much will be left.

Re-evaluate what you want from the car. Do you want to spin the engine higher for the sake of saying you have a high rev limit? If so then please educate yourself on shift points and where you actually want to shift a car for maximum acceleration, and have a look at piston speed vs connecting rod load, for an appreciation as to how enormously stressful and potentially destructive high RPM operation is to an engine. Do you need to spin it higher because "With 3.43 rear gears the engine easily reaches the rmp limit quickly in gears 1-3"? Practice your driving; people run 10 second 1/4 mile times with far more agressively geared cars and shifting is not a problem once you get the hang of it. Also the final drive on your car is 3.42.
Do you want to spin the engine higher because you want more horsepower? Decide how much power you want; you can get 50ish more HP with just headers and a tune, 80 more from that + a cam swap and 100+ more if you do that with ported heads. If you want even more you can supercharge it too; one of the nice things about supercharging is that you don't have to spin the engine higher to make power, so it is a lot easier on the valvetrain, oiling system and the bearings.