1988 Jimmy with a mild 383 and AVS2 650. Very happy with how it runs. Took it from Wyoming to Minnesota this past summer and averaged 16.5 mpg trying to keep it at 75 mph. Put a wide band 02 on it after I got back and was able to lean it out a touch and it got me about 1 more mpg. Best I've done is 18.5 on a 120 mile trip at about 70 mph. It has great power with no bogs or hesitations. I also have a 2006 avalanche 2wd with the 5.3 that I had to build a trans for this summer (after it had sat for a few years after my son blew it up towing a couple 4 wheelers in the Bighorn Mountains), so I started using it to pull my band trailer and the first time using the Avalanche I was wondering it I was ever going to get up to 70!
I also worked a bit on the Jimmy's timing curve. I think that really helped. Anyhow. I really like the AVS2 for driveability and simplicity and do not miss the q-jet I had on it that was built by a very reputable builder.