First thank you for even reading this. I don't want to be that guy but I am today.
Engine is a 2003 L59 5.3 out of a Yukon. Its on the stand with the stock rotation assembly already in place. I will assemble the top end this weekend. Here is where i am 100 percent completely lost. I can assemble this engine, hook up every wire and sensor and drop it in.
Now the tuning part. I have read and watched until I want to puke. I have the original harness and ECM for this particular engine. I did not leave it stock, Here are my upgrades and what its going in.
1987 Chevy 4x4 Square Body. Manual transmission with air-conditioner.
Texas Speed Stage 4 cam 223/226 .600"/.600' 111LSA
TSP .660 Dual spring kit, upgraded rockers(trunnion) Gm LS7 lifters everything else was replaced but with stock/summit components.

Once this engine is assembled and everything is hooked up what the heck do I do? How does this "tune" thing work? I read about send us your ecm and we will send it back ready to go. Now I don't want to sound stupid here but hey I don't know, so do you fill out a card or something telling them what you have and what you have done and they basically program it to that spec and you are good to go? Because if that sucker is not plug and play I am lost. I have been looking at stand-alone harnesses systems that include an ECM (Aces) that comes with a handheld. Well when someone is tuning your ecm do they have to know the exact specs of your cam or do they use the stock, mild or wild button like I saw on an Aces video. Would my engine even crank with the stock ECM. I need the boot to the behind approach on this. No kids gloves, I am 55 retired and working on a second one so let me have it.

Thanks, Ole Buck.

 

Most of those '87 came with really high axle gearing.
223 cam, manual trans and heavy-ish vehicle is going to take a lot of iteration to get good drive-ability in the "let out the clutch gently zone"
Thus, I strongly recommend that you obtain HPTuners, and a $50 dollar laptop off Ebay and take charge of your tune.

 

Thank you. I failed to mention that this vehicle has an 8 inch lift turning 38's with 5.13 gears . Its not a grocery getter.
And I still do not understand what is meant by "obtain HP tuners" What is that and what does it do. This is new to me and I don't know the lingo.

 

With that Stage-4 cam you haven't just dipped your toe in the water, but rather jumped into the ocean with a 20 ft wave coming.
From what you have said, I suggest you start with a "mail order tune" where you send your PCM to a reputable tuner (plenty here on the forum) with your full engine and transmission specs and your personal goals.
Unfortunately that likely won't be enough....
You likely will need to buy "HP Tuners VCM Suite MPVI3" with at least 2 credits for about $600. You install it on your laptop and connect to your car with the OBD2 connection. From there you can install new tunes. More importantly you can create a log of all the engine parameters while driving which can then be sent to your tuner who will then adjust your tune, send it back to you via email and have you install it on your car with HP Tuners. It will take several iterations.
For this to work, you also need to:
1. Install bigger injectors. People here can give you recommendations.
2. I highly suggest you install a wide-band O2 sensor/gauge in your exhaust which will connect to HP Tuners and creating those important driving log files. I like AEM gauges.

If all this sounds like too much, go back to a stock camshaft and then the stock tune and the stock injectors will all work just fine. Do you really need more than 350 ft/lbs of torque in your rock crawler?
On the other hand, since you are retired, this can keep you quite busy and mentally engaged for the next year.BTW - I'm 68 and all this stuff is my crazy idea of fun.

 

Thank you sir, thats exactly what I needed.

 

This book gives a great overview of what it means for an engine computer to run an engine, and what "tuning" is all about:

There's basically three phases to the process:

1. Get it to start and run. Get it firing on all cylinders, even if you have to hold the throttle open a bit at first. This can be frustrating, but with a little luck you'll have air, fuel, compression, and spark in every cylinder right away, or with just a bit of troubleshooting. On top of that you'll need to get the fuel injector settings, MAF scaling and/or VE tables in the ballpark.

2. Get it to idle and drive reasonably well. This requires fine tuning the aforementioned stuff, plus a few additional tables that manage the idle speed, idle spark timing, and idle airflow. Mostly just takes a lot of testing and tweaking, and probably some reading and Q&A with people who have been through it before.

3. Get it to make good power, safely. IMO this requires a dyno. But if you can bring a driveable car to the dyno, your tuner can focus on actual dyno tuning, rather than troubleshooting.

 

Hey Buck, I'm browsing some posts looking for a stock tune for my 2003 Suburban L59 Flex Fuel. I came across your post and wondered if you made any progress in your search. My Suburban got tuned on a Dyno, not sure of much, it was a while ago however I did cam it, and added cold air. I could send you my tune to review and see if it helps you think your problem through.