Inconsistent Physics Issues

I’ve been running sandbox servers for a little over a year now and admin’d a couple for 4 years prior, so I’m pretty familiar with the game. A couple of my servers have gotten pretty popular but there’s a very specific issue that drives a lot of builders away, and I’m pretty sure it’s a LUA issue.

What happens is, prop engines won’t function properly. On other servers prop engines generally operate fine; they’ll rev up and do their thing as well as you’d expect. However, on my servers, across 3 different machines, different admin mods, and different physics settings (default and not,) I have the issue of ‘RPM bouncing.’ For example, an 8000 RPM prop engine will rev up to 7000, dump to 6000, rev back up to 7000, and repeat. The same engine will function normally on a server with default physics settings, revving to 8000, so I know that the issue isn’t with my speed limits. I’m tired of this single issue driving builders away and my usual helps are stumped, so I’m here.

The servers are running on a Xeon E3 1270 3.4ghz. Tickrate 66. I don’t know what other information to provide, so ask for it and you’ll get it.

EDIT: As far as addons go, I stick solely to the bare building essentials (tools, ACF, Sprops, etc.) This issue predates all custom addons I have (which would not affect physics in ANY way.) I have tried multiple fresh installs and variations of Wiremod (with and without Wire Extras,) and removal of my admin mod. The issue persists. The only addon I haven’t tested this issue without is ACF, but since other ACF servers don’t have this issue, I didn’t see how ACF could possibly be the culprit.

Desperate bump.