What axle gear??

[dssking]

If my 88 coupe is spinning 2000 RPM at 110-115 kph, (Km, cuz I am in Canada), what rear end gear am I running?
RPO code shows a 3:55....I dunno...revs a little high...

 

[vader86]

Is that in an automatic?
Whats the RPO code.