Camerad: Hi. I have only played this game with Windows XP, so that is all I know about if it makes a difference (something I would not know). I use a dual boot setup (or whatever) so I can play old games with the real WinXP instead of using the compatibility modes (or whatever) on the newer OS. Just so you know what I am playing this on in case it matters.
Anyway, I only have the old Gold Edition of Interstate '76, not the GOG version. I use Zeus nGlide, which makes a picture that looks best to me among wrappers, and offers high screen resolution.
My version of I-76 includes support for two joysticks in addition to the mouse and keyboard. I play this game using the mouse, keyboard, Logitech G-27 (steering wheel, shifter, and pedals - it is all recognized by OS and game as one controller), and a Logitech Wingman Extreme 3D Pro joystick, which has many programmable buttons, allowing me to steer with one hand and press commands on the joystick without looking, which seems more convenient to me than using the buttons on the G-27's shifter.
For me, keystrokes, etc. programmed to buttons on the USB game controllers are recognized as those keystrokes, etc. in the I-76 game. And the game controller buttons, when not programmed, are recognized by the game, which allows the game commands to be remapped to game controller buttons per button number.
Sorry if I just wrote too much of what you already know and stuff you did not ask. That is what I am able to do with the Gold version of this game, though. Good luck.
[EDIT] I forgot to make sure to mention that I am using the pedals of the G-27 for the accelerator and brakes in the game. That and the steering wheel control input are proportionate to the physical input. It works really well to control the cars. It is not just steer right or left or not at all, It is gradient or whatever (sorry, I do not know words for it). You can turn as little or as sharp as you want. Same with the G-27 pedals. It is not just all gas or no gas. You can speed up and slow down according to how far the pedal is depressed. Pretty cool really. Nice simulator for such an old game.
What did you program your g27 controller to? Up/down? I can't get mine to work at all in the game