Contact Jayco. I had the same dilemma earlier in the year. I thought what they told me was too high, as did the tech when we picked up the trailer, but the shank I got based on what Jayco told me was right on the money.
Mike and Kim
Current TT: 2012 Eagle Super Lite 308RETS
Current Hitch: Equal-i-zer 1400/14K
Current TV: 2010 Chevy 2500HD, CC, LB, Duramax/Allison