my 2000 s70 went from about 400miles a tank to about 200 very quickly. currently i have 102k miles and have all service intervals done at a dealer, next one is due in 3k. recently i had a transmission issue(almost no fluid and it was pitch black), i had it all drained,flushed etc. the car still seems to be a bit sluggish, the tach goes up a bit now and then, can this be related?