Trans coming out of gear in 5th full throttle

While riding bike recently on highway I noticed when bike is pinned for a few seconds it pops out of 5th gear. I've heard of these doing this in 2nd gear mostly but I don't think I've ever heard of them ding it in 5th. 83 KZ1100 22,000 miles. Is this bent shifting fork ? Bad synchro out gear normally? This isn't a huge deal as cruising in 5th no problems

I'd suspect a bent shift fork first..... Steve says the KZ1000 shift forks are thicker... I've never held two up to each other to see.
Could be a worn out drum too... ?

Motorcycles have constant mesh transmissions so no synchroes. It does sound like you have either a bent shift fork, worn shift drum or damaged shift dogs and slots. It will never get better so I'd start gathering parts and tools. This sounds like a good winter project.

Probably not a job I'll do myself. I have rebuilt a few top ends, pistons, cams and such.. But I was younger could see better ,thinking messing with trans not in my comfort range. But I'll research the job a bit more.

Could be a detente spring. Also they made changes to the shift locator and locking arm under the transmission cover. It's behind the clutch/sprocket housing. I'd start there. If you can do a top end, you can surly do the tranny. The only change to the shift fork was the large one. The other two are the same. I'm not sure about the J ones.
Steve