300tdi doesn't hold boost

I brought a discovery 300tdi a couple weeks ago, been running fine then the last week it been lacking power up hills if it's hot and, you it show it any type of hill it doesn't hold boost at all, boosts up then drops off again. Since then I have cleaned the intercooler, changed all the pipes still doing the same, but also have noticed I have a small leak around injector one on the engine, don't know if they are related in this problem at all.
Cheers in advance jp