hes right, i have richmond 3:73's and an auto on my 88 and at 90 it shakes like a mofo and turns about 3250rpm's n i hate it but i love it off the line:) i use gas in that car way to fast, about 144 miles per tank on average and even worse with highway miles

is your car dropping into overdrive? is teh convertor locking up? is your service engine light on?
that mileage is a sign of something other than the gears. and the shakign has nothing to do with gears.

later
tim