To be honest they sound too big for you. If your needing to do them really tight to stop it from feeling like your foot is coming out of the boot, then thats a good indicator that the boot is too big for you.
It's that fact which is more then lickly the reason your getting shinbang.
Did you actually have the boots fitted in a shop?
Your best bet is take them to a shop and see what the fitter there thinks of the fit. Get them heat molded, but be prepared to pay if you did not buy them there. Also a custom footbed is a good idea, but see if the fitter thinks its worth working on the boot or weather you should start again.