I've had the same problem that was eventually traced to a throttle position sensor with a dead spot just above idle . One more thing to check !

Settings are one reason. Main reason for it though is backlash in the drivetrain. The gears smash together pick up all the slack because of the collision they go back, collide with the other end then repeat. You add an engine, some gas pedal action, and an extremely low gear and that's what happens.

Have you adjusted your tps?

if I had this issue, I'd have fixed my idle control and accel enrichments (accel-pump and EAE) by now...

I asked for advice and got it. In the meantime we have had some very cold weather and snow. As I have a winter vehicle I don't drive my car in snow or on salty roads. I drove it around a bit yesterday but didn't have time to screw with it. I likely will work on my idle and settings on Saturday.

Thanks for your help all.

Bracing your right foot against the trans tunnel can get rid of much of it. A lot of it is due to it being right at that resonant frequency where it's affecting your foot on the gas and you're trying to compensate and you end up looking like a tool. Bracing your foot so it can't move can help it a lot. My car has always done it sometimes, and my diff & motor mounts are both new last spring.