Mike, our 603s don't have the banjo bolts on the overboost protection circuit. On the passenger side of the intake manifold, there's a nipple with a hose connected to it ... that runs into the bottom of a box on the passenger-side firewall called the switchover valve ... out of the top of that runs a line to the ALDA on top of the IP. Clean those puppies out ... or replace them ... the plastic line is cheap and can be bought by the yard at a dealership. Mine were brittle and snapped when I tried to clean them, so I replaced them. If your car is anything like mine was, you'll have black gunk in those two lines and all over the nipple on the intake mani as well as the switchover valve. Clean all that up and you may notice an increase in boost. Don't think that would cause any hard shifting, though ... like babymog said, check all vacuum lines for leaks.

I'll try to find some pics of the overboost circuit for you tomorrow ... I know I took a few and hopefully they are still on my laptop at home.

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)