boost leak is not just in the turbo housings, you may find them on some of the pipine, go around and tighten all induction piping, look for oil leaks on pipes due to blowback.
Just go over every thing logicaly. Boost leak = piping, sprakplug gaps, coils really blocked air filter say you have a big fat rat in there when you boost no air for the motor = no power.
Slipping clutch.
last thing i can think of is it simply was to big of a hill and the poor car ran out of puff.
Oh one more thing, stock bov and internal gate check to see if they are stuck open.
See if you can get to full boost on flat road, after checking everything else.
another thing turbo may be d o a.