Before doing anything I would look at the current engine condition. Check everything out and get her tuned up, getting the most out of what you now.New plugs, wires MAF and intake bypass have and blade cleaning. Maybe go with a little hotter plug given your mileage on the engine. Check out your current cat and ensure it's not restricting exhaust flow. If it is this a good reason to do the complete exhaust and upgrade, given your mileage again this could be your biggest bang for the buck.
If you know someone that has or does dyno tuning take it there for a before and after just for fun and knowing a starting point. The cat can be checked by exhaust shops with a flow meter made for this check. They drill a hole before and after the cat and check it's flow. Another way to tell if one is clogged is the sound. If you truck sounds like a vacuum cleaner out the back when you step on the gas it's most likely the cat is bad, it will also stick a little and the exhaust once the engine is up to temperature even at idle will be too hot to hold your hand up to......about 15 seconds and it will feel like it's going to BBQ your hand. Hit the gas and it's going to blow extremely hot air and you will not be able to hold it there at all.
Also check your intake system. Make sure it's clean; get the dirt out of the air box bottom or where fresh air comes in. Make sure the intake path where it's getting fresh air from is clean and free of leaves, mud trash or what ever else could been lodged in the area to reduce airflow.
Given your mileage your injectors could be working but might not be working as good as they should. They should have a nice spray and not be clogged. There are places you can take them too that test the pattern and rebuild them for a fraction of what new ones cost, I would try this before buying new ones or going with anything other than GM ones unless your going for higher output. New injectors could be and expensive purchase and the getting. Do some research on any brand your looking to buy and see how they have held up for others. Some of the garbage the AutoZone and others sell is just as bad as having a poorly working stock GM injector.
Your plug wires could be a cheap and very worth while change. Old wires end up having more resistance and reduce then energy getting to the plug. Since these wires are short and direct fire from the coil this is not as much of a problem as it was in vehicles that have longer wires but people keep wires on longer now. Thicker and fatter wires don't always mean more energy. I would go with a proven brand or GM wires, MSD, Taylor or Autolight in what ever color you choose. A shop should be able to check our coil packs output too ensure they up to par. They will go bad and loose a little over time. Most of the time if one is going bad it operates hot, when the temps go up the performance of the coil goes down and you loose energy to the plug.
Also you should check engine condition with compression and leak down checks. Compression at all cylinders for optimum results should be within 10% of each other and above 125-130 PSI. A leak down will let you know where the wear is at, rings, intake or exhaust valves.
At 150,000 miles all these checks will give you someplace to really start. Tossing money at a bad engine will be a money pit. Taking a good engine and giving it new life is a great start and then go for some upgrades after your current stuff is good to go. Your going to get the most bang for the buck this way.
Good luck with your project.
Joe
