2014 sr viper xtx will not go in reverse

[SudburyApex]

Check belt tension also. If it is too tight, it creates a load on the two gears that mesh, and they don't want to slide apart.

interesting. I've never touched the deflection on this machine. Although the previous owner switched the belt to an 8DN. Hopefully it was machined...

 

[74Nitro]

interesting. I've never touched the deflection on this machine. Although the previous owner switched the belt to an 8DN. Hopefully it was machined...

With the 8DN belt, the belt will be above the secondary sheaves higher than normal, which is ok, just make sure it isn't too high. Usually they squeal at idle if they are too tight.
This may not be your issue, just giving you something to check.