I have the ECM from my old (sold) Suburban. The computer was modified by Wester's Garage in Canada. This was from a 1999 k2500 7.4 (454) truck. It may fit more, but you need to do the research.
They made the shift firmer, upped the timing while still running on 87 octane. I did get a little better fuel economy, and it shifted awesome. Great for towing.
They charged me $ 290.
You will have to re-learn it to your vin, but that is a simple process ( 10 minutes). You will also need to swap the knock module out of the original computer.
Asking $80 and shipping from Charleston, SC
Thanks, Ricky