I finally finished reading this thread "from cover to cover" because I have a transmission issue. I pop out of fourth when I'm really pouring on the coals. From neutral to first is a crisp clack. First to second is a perfect audible clack, but you don't really feel it. Same into third. Where it gets interesting is third to fourth doesn't feel so smooth. What I mean is when I lift my toe, it feels like there's a detent or a notch in the shift action. I get this by just barely pulling the clutch, rolling off the throttle, you know, normal stuff. If I get on it at this point, it will pop out around 6500 rpm. I pay attention and when it makes this crappy shift, I plunk it back into third, and then deliberately shift it into fourth with a crisp flip of my toe and snap the throttle off a little. I will hear it clack into gear and all is well... most of the time. Fifth doesn't really give me too much trouble. I have noticed that my trans doesn't like to be shifted gingerly- it likes the faster toe movement.
When I go out on a casual ride, nothing too crazy, I never have a problem. I don't want to crack it open because for now this problem keeps me out of trouble. 
Anybody have any comments?
Ron, any updates on yours?
This is usually caused by some damage to the "R" shift fork, but the CAUSE of the damage should be located or it will reoccur. One common cause is a leaky O-ring in the countershaft bearing retainer, which routes the oil from the countershaft up to the mainshaft: the mainshaft is last in line for oil from the pump. The O-rings are getting old now, and should be replaced. That part is easy.
If the oil supply is low, the gears don't slide well on the shafts, side-to-side, into each other. This makes the fork push harder on the grooves in the gear. This both widens the groove and wears (or burns or bends) the fork over time. The repair is to replace both the fork and the gear it is moving back & forth. Try to find a used gear and a new fork, for best results. The "F" and "K" bikes share the same parts, here, so any tranny will be a good donor.
Interestingly, the final drive gear ratios on the "F" bikes, combined with their higher powerband and the U.S. 55 MPH speed limit for 20 years, makes your symptom the second most common failure in the "F" and K7/K8 gearboxes, because at 55 MPH in top gear, the bike is off cam and slightly sluggish: popping down to 4th for spirited hiway passing is/was a popular "F" sport in the day. That gearset then got shifted much more than on the earlier "K" bikes. This was also found on the K5/K6 bikes (with impatient riders) because of the overgearing and loss of top-end power those bikes had. I usually "fix" that by installing the 17T front drive sprocket.
