I had Horizontals in my Lance...they worked very well. You do need to keep the fittings clean and make sure the seats are good, and any rubber bits not worn. At 2009 it should be hand tighten type, if not make sure you tighten everything. Also you said it has new stuff...did you do that? It may be best to go see a good dealer, the new stuff could be bad or maybe not the correct unit, not likely but starnger things...
Post some pics of the tanks and the new bits.
Good luck and don't give up on those tanks, once they work, I think you'll like them. I wish I had them on my present TC.
BTW is the a 150 Yamajammer hanging on that sleek craft?