There are a lot of options for getting more speed, different rear gears, auxiliary units, etc...
You should be getting more than 35mph though...I'm guessing you can fairly accurately judge speed and don't just have a poor speedometer. Remember your speedometer will read slower than actual now. Your 8.25 were 37.6" tall with 536rev/mi and your 9.00 are 39.16" tall with 515rev/mi. It's not much difference though, so I too would believe your rear in actually in low. Have someone pull the switch and listen/feel for if your shifter motor is actually working. You can always unbolt it and visually check if it is moving as well. You should be able to move the rear axle shifter by hand with the motor off to manually shift it to make sure nothing is hanging up. If It's vacuum you can easily visually check if the shift arm is moving or not.
You could also jack up one wheel and spin it to see what ratio you are actually in. If you tape a piece of string to the drive shaft then spin the wheel you will be able to easily count how many revolutions the drive shaft made. I think the drive shaft will spin twice as fast with one wheel on the ground...but that will be easy enough to tell as nothing has a 12 or 18:1 rear
Tad
