HighAlititude Prop '04 wakesetter VLX

I have an '04 Malibu Wakesetter VLX that I bought a few months ago from a sea level owner. I live at Lake tahoe (altitude 6300 feet). I have the 340 Indmar Monsoon motor. Current prop is 13.5 dia x 17.5 pitch. I know i need to downsize my pitch especially, but does someone have a strong recommendation for prop size.

For reference:

'07 Malibu wakesetter vlx high altitude prop option from their website is a 14.5 dia x 14.25 pitch.

Dealer #1 phone call recommendation: 14 dia x 14 pitch

Dealer #2 phone call reommendation: 13.5 dia x 16 pitch.


Additionally, according to my perfect pass I'm topping out around 35mph right now - this seems rather low to me, wondering if it's most likely a prop issue or miscalibrated perfect pass. I know I should lose SOME top speed due to altitude but this sounds larger than I'd expect....

Thanks all...
Fred}