I would try disabling L2 cache for starters or if that still fails, L1 cache (as a test, obviously, you would not want to run without it under normal circumstances ) .

I had a very similar error with a faulty video card

Disabled the L2 and L1. I thought it worked at first because i could enter DN3D setmain.exe, but it crashed and after restart i got just the same error.
Ahh hope its not the video card 😒 I will try a different CPU, I have a few of those, but VLB video cards not so much. I have tried to change slots for the video card also with no effect. I have one more slot to try tho.

I have a faulty isa card, it would happen only on duke3d, quake and doom would work I was positive it was the system. Changed cards and worked, tried the faulty card in a different system and got the same error on duke3d.

Those dos4gw errors are to do with memory so usually ram or video ram

I will take a closer look at the card. Is there some program that will do a video memory check?
Maybe I should reflow the solder on the vram, but that might be a shot in the dark.

not sure about any dos diagnostic apps, quickest would be to try another card or try your card in another system, but if you have 1 card and 1 system then yeah ill wait for somebody else to recommend any dos diagnostic utility