2006 XC60...80k miles...I feel that the car is 'in tune'...had dealer recently scan for any issues, none noted (I had a last visit before the warranty ran out). Took a nice 250 mile drive yesterday...mostly Thruway and back country roads....no stop and go. Averaged about 18mpg. I really thought I could break 20. Recently did the PCV system, cleaned the throttle body...obviously didn't help. It idles and drives smoothly. Could use a tad more power, as my other XC70 (2004) is noticeably quicker.
Any ideas?

Two years ago, my '08 XC70 needed a new vacuum pump at 78K.

Could this act like a vacuume leak?

Not really. The vacuum pump is there to check that vacuum can be attained. Some newer cars use it so that the brakes work even with the engine off (key on).
--
Keeping it running is better than buying new

You should have 24+ on a day trip like that. This time of year, check your tire pressure as it will loose 2 psi for every 10F drop.

You obviously have a manifold leak - somewhere. I assume you have the 5 cyl engine with a low pressure turbo. There are a lot of vacuum lines! Check the obvious ones at the front of the manifold, then the ones around the boost controller (4) and the turbo (3). Grab each of the intercooler lines and try to twist them, if any move even a little bit then tighten the clamp. Same with the air attachment at the throttle body and air cleaner.

At 80K, how old are your Volvo spark plugs? Are they clean?

The dealer should have put your engine on a scanner and checked the fuel and exhaust sensors. But a lazy mechanic won't bother. If it ain't broke...

--
Keeping it running is better than buying new

Thanks Klaus... I did the PCV, had to remove the intake manifold twice due to a mess up on my part. I used new gaskets each time. How do I check for manifold or vacuum leaks? Is there a DYI way to do it?

I have tried butane, cigarette smoke, etc. If the leak is large enough, those work. Usually, it is the smaller leaks that cause MPG problems, the engine management adds fuel to make up the difference.

There is no easy way. If you cleaned the PTC nipple on the intake before the turbo, make sure it is seated tightly. As for the intake manifold, all you can hope for is that the bolts are all properly torqued, and you started from the inside and worked your way out.
--
Keeping it running is better than buying new