4L80E tuning questions

Hello, I am a savvy mechanic having been a tech for about ten years. However, I have very little knowledge on the logistics of tuning. My truck is an '01 2500HD 6.0/4L80E I bought with about 90k miles in May 2018. I didn't know at the time, but it had a Jasper trans. Long story short, I had the trans replaced TWICE under warranty since purchase. I put on all new lines and a new cooler. I think the problem was just poor build quality by Jasper - NOT SURPRISING. Anyway, I think the trans I have now is a good one.

I use this truck for hauling and towing. I pull a 16' car trailer with various cars on it from time to time, so it's pulling maybe 7k lbs sometimes. I want good performance and longevity. I understand it is common practice to partially disable torque management, up to 65% or so. Is that still recommended when I'm actually using the truck as a truck? Is there anything else I should change to improve the truck for my purpose, like locking the converter in third, or increasing line pressure, etc? And finally, what product do I need to do this? I understand I need the tuner module, cables to connect my laptop, and the software. What kit or bundle do I need? Plus I need some "credits?" Unless I could use a product to also tune my '90 Cadillac with a TBI 350, this truck will be the only vehicle I'll be tuning, for now at least. Thank you!

I have another question. If I floor it going around 45 mph for example, I get a 4 to 3 downshift almost immediately. But, that doesn't do much, and I don't get the 3 to 2 downshift until 2 or 3 seconds after the initial 4 to 3. Is this normal? And can this be rectified with tuning? It's really frustrating when I actually need that extra power every once in a while. I never floor it when it's loaded down or towing, btw.