break system

hi everyone...my names alan and im a newbee on this forum.....ive got real issues with a 99 hijet van i brought a couple of years ago it failed its mot on not enuff break presuer..and the headlites were to dim so i garaged it in march 2019..and been buying all new part for it since and installing them as i go...ive basicy replace d the entire break system...new master cylinder...new slave cylinders..new breaks all round with new drums..and discs....stript down the l.s.p.v. and rebuilt it.....bled it by the book....and still after all that the break pedal gose about half way down before the van slows down and even if you jab the breaks to get a short sharp stop it wount.....can eny one help me please...i dont know what els to do apart from sell it and im desperately try not to want to do that im even considering replaceing the lspv for a tee-pipe just to rulle that out as its the only part of the entire system that isn't a brand new part.....