Denis,

are both leeward and windward telltales flying when you have problems with speed/power? Do they stop flying and stall when you let off the downhaul and sheet?
What is your mast rotation like, and your leech (leech telltales flying or stalling)?
You write you have been sailing for 15 years so I assume the telltales are all flying, but I have to ask just to make certain we are on the same field.

What cats or boats have you sailed earlier?