I've recently resurrected a '99 F4, 2800 miles, mint. It's just been sitting for over 10 years.

I've had the carbs cleaned and balanced, the rusty fuel tank clean and coated, changed the plugs and oil, and new fuel filter. The bike idles just fine and revs fine while stationary. Under 50 mph, the bike runs fine, but once on the highway, the bike hesitates badly (at any throttle position).

First gear seems fine as it revs through the entire range,
Second gear there is only the slightest bit of hesitation,
Third gear has noticeable hesitation,
Fourth and fifth are a nightmare and the bike actually slows down once in 6th and if you pull in the clutch in any of the last 3 gears, the bike stalls. It does, however, start right up as soon as you bump the starter.

Any ideas? could this be old coils that may have gone bad or possible a weak fuel pump or a vacuum leak somewhere or perhaps something to do with the solenoid valve under the fuel tank for air injection?

I've seen others have this problem on this forum, so any input for how they resolved it would be appreciated as those threads do not reveal what the cure was.

Thanks in advance