Hmmm. Flickering. I guess "flickering" needs to be symptomized...what's actually happening?
As in the "light" on the tach needle is going off and on? Or is the needle in fact quivering about a few hundred RPMs?

Light? No biggie. Call the dealer, inform them that they botched something and you'll get back to them after your trip. Hopefully it's just a connector that isn't seated all the way.

Or "flickering" as in needle indicator quivering +/- couple hundred RPMs?
As long as the tach needle is, in fact lying.....as long as you know that the engine isn't actually doing that as a result of the modification, you'll be safe - but maybe an intermittent connection can burn out an indicator part?
If the engine is unusually varying in RPMs with a constant throttle setting - especially after a cruise control installation - I'd get it checked before the trip. Again, either way, hopefully it is a connector that isn't seated al the way.

Best of luck.