I have a 99 5.3 xcab Z71 truck with about 112,000 miles on it and it seems to be getting tired. I am losing power and gas mileage. I have no interest in buying a new truck, so I thought I would do some changes to my truck. I searched in here and found a few tips, but still haven`t answered all my questions though. This is my daily driver and it`s not a performance truck nor do I offroad in it. I just need some more lowend grunt, not highend horsepower. I also don`t want to do FI. Do I rebuild the 5.3 to get more power out of it or do I put a 6.0 in it? I just purchased a set of 05 LQ9 heads cheap. If I do the 6.0 install, then what can I use from my 5.3 to complete the 6.0. I don`t plan on buying a complete 6.0. Just block, crank and rods and then a new LS6 ported oilpump, timing chain, lifters, cam, arp bolts, eutectic pistons. "042" 200/208 .500/.500 115. That`s the Vinci cam I was looking at. I don`t drive my truck hard, but do a little towing with it. It has 3.73`s in it now, but I need some power. I have a 67 and 69 camaro that I am restoring and I also have a 01 ws.6 trans am that I play with, so money is a concern on this build up. What is your input on my delimna? TIA

 

Try cleaning your MAF sensor elements and resetting your PCM. Is your air filter new or OK? Have you done a compression check?

 

I just cleaned my K&N filter the other day and cleaned the carbon off the throttle body blade. I have not cleaned the maf though. Truck runs good oil pressure is strong, so I doubt it`s losing compression. I increased my tire size to 285 a while back and that is mainly what killed my power and gas mileage, but it`s starting to drop even more now. I am also experiencing vapor lock as well. Think it needs a new fuel pump. I hate to go through the expense and time of building and installing a new motor, but I NEED more power. The truck never had enough power for me anyway. If there are alternatives to not putting a new motor in, them let`s hear em. I`m all ears at this point.

 

Clean the maf, especially after oiling the K&N filter. Cats may be cloged, so you may want to remove or replace them. If your going with a 6.0l your going to need to replace the injectors. 99's have 19# injectors and 2000 and up have 24# injectors. I have a set if you need them. And last but not lease replace the 99 pcm with an 02 pcm and get a custom tune from Nelson Performance or one of the other sponsors.

 

I agree with the above plus the 02 pcm and Nelson tune.
112k is lots of miles on the cats. I would replace them.

 

What`s the difference between the 99 and the 02 PCM? Are you saying to put that on my 99 with the 5.3 in it?

 

The 02 pcm is just alot better plus a custom tune will help alot. Replace the o2 sensors and cats and you should feel a big difference in performance and mileage.

 

You talked about Vapor-Lock, It would be a good idea to replace your fuel filter which usually causes those symptoms. If that don't do it, you might even be looking at a fuel pump.

 

here is some info on the 02 pcm

 

Ok, so I get an 02 computer and have it tuned. I throw the cat in the garbage and fire up my welder and build a dual exhaust. No emissions check in my state. Put something like the air raid intake setup and port the throttle body. Put new O2 sensers on. Already have put a fuel filter on and have already made plans to put a new fuel pump in. Put 24lb injectors on. I don`t really want to deal with headers. I hate them. What about the LQ9 heads I have? Mill them and bolt them to my 5.3 or put them on my T/A or put them on my 69 LS1 camaro? Do I have too many miles to put a cam in?