I suspect your compression gauge is off . . . A healthy 2.0L merc is generally 115 - 120psi. B/c all the cylinders are even and the motor starts easily and runs . . . sounds like a bad compression gauge.
A bad stator will cause the motor to run rough/misfire above 2500 - 3000 rpm (high speed coil). A bad switch boxes will cause one side of the motor not to fire.
A bad trigger can cause one or more cylinders not to fire, but they almost never fail (unless it's the sheathing on one of the wires).
Coils can fail . . . check grounds and make sure plug wires are snug.
If you have the idle stabilizer connected . . . you might consider removing it. Read why on screamandfly.com. Also . . . oil injection is problematic on these motors (2.0, 2.4 and 2.5L mercs). Merc makes a plug you can buy specifically for folks that want to remove the oil injection.
If you are concerned about high speed jets on the carbs being clogged . . . you can pull the cowling and the air box cover off the carbs and have someone else drive. Get on a plane (faster the better) and look down the throats of the carbs . . . you will see a nice fan spray of fuel. If one differs significantly from the other 5 . . . you likely have some crud blocking the high speed jet. If the spray is very different on one cylinder . . . back off and drive home at low speed and pull apart the carb with the issue (you may want to do all of them).
Is there a strong smell of fuel or any noticeable fuel leak? when you remove the cowling?
Did the motor get HOT? Are there any wires that look like they melted?
a bad fuel pump usually causes surging at higher speeds . . . if you pump the bulb while running it will usually overcome problems with low fuel pressure or a weak pump . . . then you know you need to rebuild it.
online merc manuals
http://1manual.com/Mercury%20manuals/intro.html
unfortunately they don't have anything back to 1988 . . . just 1992 and newer. There will be some relevant information in that manual.
http://1manual.com/Mercury%20manuals...52r3/cover.pdf