split rear-ends?
 

has anyone ever heard of a split rear-end for an FJ40? i wanna go faster on the freeway than the top end of 60 mph

you mean a two-speed? no, ive never heard of one in those

I can easily get my fj40 up to about 70 on flat highway. Hit even a hint of hill and its a different story, though. Stock engine and drivetrain.

you need an overdrive unit

Larger tires would help to get faster highway speeds. The Stock 4.10 gears are a bit low for a daily driver. In town with the stock motor and larger tires would not be fun on the clutch. I can go faster than the speed limit in mine (around 110 top speed but is very scary and not recomended) But mine is far from stock Bigest mod being the Chevy v-8. Sounds like an overdrive unit would be the way to go.

or a 5speed swap

a 5 speed will run you about as much as an overdrive...