There is no "sure this is great" or "no this sucks".
All depends on what you want to do. You could have different gearing than someone else or any of a slew of things. You really don't have anything that isn't simple to fix but then again the AFM is not done well on the 2007-2008 if it is done well at all ever.
If your going to spend the money to boost up your trucks power level there are a couple different routes.
Just rebuild your 5.3... But realistically nothing really wrong with what you have. A little oil every so often is cheap compared to a new motor.
You might be better off watching the junkyards for a 6.0. Sometimes they can be had cheap. Does your truck have flex fuel capabilities?
Personally if I were to do it I would buy a junkyard 6.0 and have THAT rebuilt. If the total cost starts getting close to $3000 then you should consider a new engine from a place like ATK Performance engines which has a 6.0L engine they can build for you that gets a whole lot more power. The 6.0 and 5.3 engines are both LSx based and everything from your 5.3 should bolt up to the 6.0. There is also a 6.2L that may work. If you change the engine size you will require a retune. If you go to an ATK engine you may need to get new injectors as well since the engine comes as a long block with no accessories or intake on it.
If getting a 6.0 build from ATK they require a block in exchange or $500 for a block. They didn't have the same requirement for the 5.3. They do also sell performance 5.3's which might save you $1000 but not nearly as powerful. But still more powerful than a stock engine and probably more powerful than a stock 6.0 or 6.2 but you would have to contact them to be sure.
Since there is nothing really wrong with your engine you have time to save up and decide... Your engine could go another 200k miles without issue... My '03 has 275k miles on it now and it still runs very strong. has an oil pan gasket leak and I had to have the heads replaced due to them being cracked (Damn Castech heads anyhow) but I would be surprised if I didn't get another 200k miles out of this engine.
These engines are pretty solid.. You COULD just get a different set of heads and a cam for your truck and get much better power, while also taking care of those worn valve guides... A freshen up like that could likely wake up the engine and get you another 200k miles easily just like in my truck. Assuming no issues with the rings or crankshaft.