The 8.1L engine with the Allison transmission can be a workhorse.
There are a few aftermarket improvements such as better spark plug wires; the OEM wires are terrible. I believe that Ed at Fast Chips used to have a tune for the8.1L. You can get tunes for the8.1L from the following:
https://www.ultrarvproducts.com/Ultr...-Custom-Tuning
https://www.raylarengineering.com/computer-tuning.html