1988 omc out drive in 21 ft. seaswirl high altitude gear change

[robsphoneone]

I have sea level gears and need no how to install high altitude gears in top of out drive. Boat is sluggish

 

[Bondo]

Ayuh,.... Welcome Aboard,..... What prop ya runnin' on it,..??

 

[Scott Danforth]

much easier to change prop pitch than gears

 

[jerryjerry05]

You'll need special tools to change anything in a Cobra drive.
I think you can buy the tools. 1500$
Do what the others suggest and try a prop?
What rpm's at WOT??
Compression test?