I recently purchased a 2018 STX. Scab, 4x4, locker, etc.
Is there a way the back-up camera can be turned on while in a forward gear? As in going down the highway?

 

I think only on the upper trims with the 360 cameras. I think.

 

Even in the upper trims (I have one), that can't be done with the stock system. I do believe that there's an aftermarket solution to that problem though. I don't have/use that, so I don't know for certain. I'm sure that a quick search on this site should reveal an answer for you.

 

When you say turned on in forward gear; the only option for that is the rear view can be set to >delay turn off< for about 15 to 30 seconds on the >rear view< while moving forward.
My 2018 XLT has that option and turned on.
I like to see it, as I don't miss the normal screen for that short time, in case something needs to be seen as I move forward.
Good luck.

 

Also if you go over 5mph it will get out of camera mode.