This may sound ridiculous, but I am wondering whether my 1992 300sl is shifting into 5th gear. I count the shifts, but starting in second I seem only to get two more shifts. What rpm should I be seeing at highway speeds, like 65 or 75, when it would be obvious that I should be in 5th gear? If it is not shifting into 5th, what could be the problems? The car has 77,000 miles and runs great. I have owned it for six months and it is my first Mercedes.