I've been using WSJT-X version 2.4.0 successfully along with JT Alert for WSJT-X version 2.5.9.0 with no issues for quite a while on my FT-991A, but I have found in long transmit digital modes the factory installed cooling fan doesn't cool the rig sufficiently. If I'm on FSKH-105 Hell mode and make transmissions up to 2 minutes long at times the radio would get very hot running only 30 watts maximum, so hot I was fearful I may possibly burn the finals out, but I have discovered how to keep it running nice and cool! The factory installed cooling fan is only about 3" x 3" and I took an old 12 volt 4" x 4" whisper fan from an old computer and wired it to a 12 volt wall wart (AC adapter) and as long as I sit that cooling fan directly against the factory cooling fan blowing outward my FT-991A runs as cool as can be! When I told Cliff, AE5ZA , the 40 meter band Feld Hell Club's Net Control station, about how my rig was running so hot he said his IC-7300 didn't get hot at all so apparently Yaesu dropped the ball on the size of cooling fan the FT-991A needs because the 4 x 4 inch fan is doing the job efficiently. If my memory serves me right I think Yaesu had overheating issues on the original FT-991 models. Anyway, I thought I'd pass this info along in case it may be helpful to another fellow ham. It's working for me very well!

Very 73,
Cliff, KU4GW