87 5000 loosing power sometimes

[Stephen Sherman]

First let me say that the car runs just fine most of the time. However 
when going up long hills (as we do to get home) it tends to loose low 
end power, and I've noticed the engine temps rising too.  Turbo boost 
seems to still be available if I downshift and up the rpms to say 3000, 
but is not happening at lower rpms (say 2200). Seems to only be a 
problem when the engine is getting hotter.

A quick check in the engine compartment did not show any missing lines 
or loose connections, but I did notice that the U shaped horn on the air 
intake has disappeared.  I was wondering if sucking intake air from 
close to the turbo might account for some of this behavior (Sort of 
doubt it, as this horn tended to fall off alot, so not sure how much it 
really was in place to work)

Thought, things to check?

TIA