Re: bumpy slower turns...you didn't say what shock you have..
But here's what I suggest..slowing way down for tighter, bumpy turns makes them that much worse...this assuming that your shock is in decent shape...think about it, If your slowing down for turns like these, it means the bike is riding on bumps for a longer period of time, hence you Feel more bumps, also along these lines, holding on tight magnifies the "bumpyness"...On a track that I ride often, there 2 slower turns that are fairly bumpy, and for the longest time, I'd slow way down for em, thena friend of mine, who isn't..too affraid of trying new things, went through those turns as if there were No bumps...and guess what, I tried at his suggestion, and no worries, no traction loss, as the bike goes over the bumps so much faster, that I hardly feel them.
Sometimes you just have to Trust your bike, which includes your tires..
My suspension is Stock, but resprung and revalved with Race Tech stuff, works really good...
As for the braking from high speeds, what you need to do is Find a reference point to begin braking, it's called a brak marker, can be anything, a cone a rock, a patch in the tarmac..ect...all good riders have em, along with other markers, a Fast rider is almost lost without them..Once you find those markers, it makes life much easier on the track..I.E. I have markers for when to start braking, when to let off, and when to start gassin it..I don't use the begin braking markers so much anymore, as I do the when to Stop braking markers. Spend a few sessions working it out..
As for your problem with Endurance...aside from gettin Old, I find a Good nights sleep, and loading up with LOTS of water, gatoraid, and banana's at least 3 days before my track day works for me. I alos skip a session after lunch, and just rest, all the time downing water, gatoraid and a good ole Monster drink..
The banana's will help alot with cramping, potsasium is good for you, I also tend to stay away from soda type drinks at the track..Oh, and I usually take 3 or 4 hard boiled eggs to eat, they seem to help a bit with energy.
Lastly, check you shock out, if it needs adjustment, or refreshing, do it..it can make a difference...
Hope this helps a bit..