97 Ford Taurus

I have a 97 Ford Taurus GL Sedan that has been a pretty sweet car. It has about 97,000 miles. I've noticed that its lost some of its pep especially on freeway driving. It feels sluggish and just doesn't feel like it goes 70 miles per hour. I recently brought it in because some times when I start it (not always) it does a jump-shimmy-shake and the RMPs jump between above 1000 rmp to dipping below 1000 rmps. My mechanic couldn't find anything wrong but said maybe its the fuel pump. Has anyone had similiar experiences?

Many thanks. :-)