When this has happened to me in the past it has always been associated with a failing clutch. The clutch is the first part of a vehicle to notice a hill.
When it slows down up hill - what happens to the engine revs? (for you to answer to yourself).
Peccavi
July 2013
I can answer this question...
my sharan runs ok with a load on a level road but slows down uphill?
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