I've been told different

[lilmule]

You wont go the same 5400 rpm with 5000 ft of elevation difference unless you have a limiter that low,other wise an rpm increase for each 100 ft due to additional air available,somewhere comes into play however since it was tuned at higher wont be able to use it all,but still an increase in both rpm and speed or a major increase in slip factor.
Normally its a sea level motor in reference to hp loss when taken to higher elevation ,not the reverse.You would still gain some bringing it down but if staying would need a tuneup at that altitude to use more of whats available.So you will gain going down some and definately lose going up.,from 5000 ft.