Ok I just tried it with instant melee, and at least the flamethrower problem is still there. So that weapon is useless in the game. If you slow down the CPU speed a lot, then the flamethrower starts working correctly, ie. it actually hits the enemy cars.

Anyway, I guess that alone wouldn't be that bad (I don't recall if I ever used flamethrower, there are more useful weapons anyway), but I seem to recall there was some kind of driving related physics problem too (due to "too fast CPU") that would manifest itself in certain missions. Maybe the info is still in the Interstate subforum.

So there's no problem; just download and run a free program that slows down CPU.

Though it makes you wonder why GOG, that wants to make old games run on modern hardware/OSes, hasn't incorporated such a fix yet.

Same thing with MM9 and some other old games. No problem for me, I just use DGVoodoo or an alternative - I can get any old game to work fine in Windows 10... but GOG should put in some more effort.

I recall that was problematic already in that old IBM ThinkPad T40 (1-core) PC, let alone modern faster PCs.

The first problem was that already then I needed to slow down the system to crawl, like that the CPU can use only a couple percent of its total capacity or something. I recall I had to slow it down so much that the game started running a bit jerkily (like 15 fps or something), but at least then the physics worked fine, including the flamethrower.

The second problem was the way that utility worked (was it CPUGrapper maybe?), ie. IIRC it would "waste" the extra CPU power, causing the CPU to run at 100% IIRC. On e.g. laptops, that easily causes overheating problems, running the CPU constantly at 100%, and it is wasteful anyway. I am unsure if CPUGrapper even works anymore on modern PCs and Windows versions.

I just tried the Windows Power Plan method, but even if I told Windows to use max 1% of the CPU capacity, the flamethrower still wouldn't work correctly. So I guess it should have been slowed down even more, but I guess I can't go under 1%.

ANYWAY, I found also this update to the old discussion:

https://www.gog.com/forum/interstate_series/updated_new_i76_arsenal_launcher_with_automatic_workarounds_2_versions/post105

It has the interesting approach that the framerate would be limited to e.g. 24 or 30 with dgVoodoo2, so I am hoping that achieves the same thing as trying to slow down the CPU? Anyway, I didn't get those instructions to work yet (I couldn't force Glide mode in the game), so I hope the guy responds to my questions in that thread.

Okay, fair enough but that road is one that I wouldn't want to walk.

I used this one: http://www.cpukiller.com/ to get past a certain part in Grim Fandango.
Shouldn't a good gaming laptop have sufficient cooling to keep running the CPU at 100%?

I know what you're saying... but a "gaming laptop" is / should be a portable desktop replacement right? Ok, I know nowadays they sometimes try to combine that with also being thin/light. I don't know what you have?

At work we have a couple of workstation laptops that have been running under full load (3D rendering CPU+GPU) and they're getting quite old now (without breaking down). But they're far from thin or light (but still "portable").

Having to tinker with old games is very much part of PC gaming. Tons of Steam games require fan patches and whatnot on modern systems too. This is all very normal. It would be nice if GOG could incorporate these patches into every game like they have with a small handful, but then people would complain they're using others work for profit and whatnot. You can't win either way honestly.

Two, one older Win7 gaming laptop that does have quite good ventilation (two fans, one for CPU and the other for GPU), and a newer Dell "generic" laptop mainly for work, but it has some GOG games installed too.

While the Dell laptop isn't a dedicated gaming laptop, it still is a bit faster for gaming than my older gaming laptop, simply because it is so much newer (it has a NVidia Quadro P600 GPU). The downside is that it does overheat easily, when running any more demanding games on it.

I read some online tech review of this Dell laptop, and they specifically said it seems to have a bit of problem remaining cool enough, when e.g. the CPU is used heavily. And I do notice its (one) fan starts screaming at full speed quite easily, especially when running some game, even an old one like Team Fortress 2.

Anyway, I wonder if there is an utility like CPUKiller or CPUGrapper that didn't try to slow down the system by over-utilizing the CPU, but instead work like the Power Plans, ie. somehow directly limiting how fast the CPU can work? Unfortunately the Power Plan approach didn't work for Interstate'76. even if I limited CPU speed to 1%, it still appeared to be too fast for the game (ie. the flamethrower doesn't work correctly).

I'm hoping I can figure out how to limit the game framerate to e.g. 24 or 30 fps with dgVoodoo2, whether that achieves the same purpose as trying to slow the system down with CPU. Not sure.

Maybe Rivatuner? You can set a manual framerate limit:
https://www.blurbusters.com/wp-content/uploads/2017/06/blur-busters-gsync-101-RTSS-framerate-limiter.png
4th setting on the right
https://www.guru3d.com/files-details/rtss-rivatuner-statistics-server-download.html

I might try, but it should be possible with dgVoodoo2 too, at least with its Glide settings.

Now the main problem is that I haven't been able to force I'76 to use 3Dfx Glide (instead of Direct3D). The instructions say it should happen with adding a "-glide" option to the shortcut, but I can't figure out how to make that work, either by using GOG's own shortcut that points to goglauncher.exe or somesuch, or creating my own shortcut directly to e.g. i76.exe.

Have copied the contents from both MS and 3Dfx to the game folder?

If you are having framerate related issues, G-Sync display is incredibly useful. You can just pick the native framerate you want the monitor to be. So usually 60 and then just enable/force V-Sync.

This allowed me to play Titan Quest with normal physics for example because it is tied to the framerate (60 being the normal behavior).