Viking range trips the gfi circuit breaker even when turned off. I tried the stove on another gfi circuit and it does the same thing. The stove works when plugged into a regular outlet. Any ideas?

I am assuming this is a gas stove.

Try it on a non GFI circuit.
If it does not trip the breaker then you probably have a Neutral to earth ground (the unit's frame) problem. May or may not be a short.

If it does trip the breaker you probably have a hot to frame short.

Do not know if you have knowledge about how a GFI works so here is an explanation.
The GFI monitors the current going in on the Hot side and coming out on the Neutral if they do not match then it trips since the missing current must be returning via earth ground (frame). It will trip with a few milliamps of leakage.

It also monitors the earth ground to Neutral connection to ensure they are separate.

Open the unit up, unplug it, disconnect a device, plug it in to see if it is the culprit. Make sure the disconnected device cannot short to the frame.
May be a device but may be something has spilled into the unit and is giving a circuit path from Neutral or Hot to the frame.

As far as I know there is not a fast way, quite honestly finding it has more to do with luck than skill.