625i starts, idles, but won't accelerate

2014 625i

Gator ran fine till last week when suddenly it would not accelerate when demanded. The engine would run rough and miss, but continues to run. It starts right up and idles just fine. I checked the air cleaner and replaced the frame mounted fuel filter to no avail, and tried a fuel cleaner additive of some sort. Additionally, this unit had a "full service" (whatever that means) done to it about 3 months ago.

I am trying to help out the owner with this and do not have continual access to the machine, nor have I owned a Gator but am somewhat familiar as I used to maintain a older generation 6x6 (?) for another friend.

This 625i machine is on a big ranch, and shop facilities etc are not readily available. Trying to get educated as to whether or not we need to load it up and haul in to the dealer or is it something basic that could be field repaired.

Thanks