Kite stacks that are large sized are usually tuned with "excess forward" (bleeding some wind pressure off the trailing edge), if the kites won't power-up you can try going towards more reverse tuning (gets the sail more square to the wind) and see if that helps. In big wind though, you'd better back off that reverse tuning or at least remember you put it there.
You fly the back kite in a stack,... read it again! The BACK kite
Label the train lines carefully for specific locations or never take them off. The more kites in the stack, the more (micro) tuning is necessary for optimal flight control. (Black-magic tuning baby, not just a ruler!)
Being able to set-up the kites upright, staked to the ground or fly them out of inverted landing is necessary, ( a friend also works!) TC Ultra handles are drilled plexi-plastic so you can "mount" the kites on a specific hole for set-up and the handles have a built in winder for your stack flying lines.
The less knots and stuff sticking-out that can grab a flying line, the better. What can you address as a do-it-yourselfer?
Stacks are a great show all by themselves!
Don't forget to breath, it's so much fun you'll be holding your wind.