Welcome. Looks like a cool adventure. I wish I could do something like that! I'm tied down to a house, wife, job, life...I love it but I wish I could satisfy the wanderlust too.
From the blog:
Usually a free flowing exhaust that weighs less than the stock system should improve fuel economy, not reduce it.
I believe that it probably won't help. An exhaust that can flow enough for making maximum power will flow completely unrestricted when driving for economy, or even when driving more normally. The same logic applies to intake, also.
The weight is also probably not an issue; I don't know how much weight you saved but the Canyon is decently hefty. All the good data I can find shows that you have to change 20% or more weight to have an effect, except maybe for certain low-powered low-torque Honda Civics weighing under a ton, and a few similar cars.
Going downhill? Back off the gas and coast. Rolling up to a stop sign? Back off the gas and coast. It's easy and free.
That's actually not coasting. That's engine braking. It may not be much
engine braking, but that's still what it is. If GM did a better job on your ECU than they did on my 2002, you get DFCO (Deceleration Fuel Cut Off) while engine braking. Mine has to do it for 8 seconds before it will DFCO. Anyway, if you're DFCOing and if your torque converter is unlocked while you do, that would be a good combination, though you'd still do better to coast
while idling in neutral (only if you're comfortable doing so). If you do use neutral, be sure to rev-match when putting it back in D.
If your truck DFCOs well then you should definitely continue engine braking up to stop signs.