722.370 auto box has issues

[Beirut Brit]

hi again
To remind some of you who aren't aware of my pick-n-mix mercedes, it's a 560 SEL which a PO has dropped a OM606 non turbo into,

What i did recently was put it back to automatic transmission after finding an auto box taken from a four speed S500

The only problem is kickdown. Or not even kickdown, just the box not dropping down a gear when the car approaches a hill.

Could this be a vaccum line issue?

thanks

MJ