Here's what I used to tell people when I sold aftermarket parts.
Think of your truck as a track athlete. Now this runner may have the required muscle to be a quick sprinter, but say they have asthma. Now regardless of how much muscle they have, they can't use it if they can't breathe.
Your truck is the same way.
Your truck has much more power than Ford wants you to know.
Now you've already started on it with the Gotts Mod.
Although, if you were to dyno test a truck with an intake and an exhaust system while you would notice an increase in HP, you would notice a much larger increase when they are combined. Rather than just the intake, or just the exhaust.
If you go back to the runner, being able to breathe in more air, doesn't really help if they can't exhale it at the same rate.
I guess what I'm ranting on about is to address your exhaust system next. Seeing as you've already started the process. I would suggest starting with a less restrictive muffler, perhaps a high flow cat as well.
Also, you may be thinking about increasing the diameter of the pipe system. This can help, but one needs to be careful to avoid losing necessary back pressure. (Hence why you never see a diesel system on a gas powered).
Note: I would not recommend this if you ever plan on using forced induction. Boost runs off back pressure.
I'm also expecting someone to chime in with more information on a tuner or chip.
You stated that it be cost effective, and tuners aren't that necessarily.
I've been up for like 18 hours, so I hope that some of that is understandable to somebody that's not in my head!