After 2 years with my Yaris I have one complaint

[why?]

Originally Posted by bronsin

A 6 speed transmission is NOT necessarily better for mileage. It all depends on the ratios. If 5th and 6th are numerically the same a six speed will use MORE gas! You have one more gear to accelerate in. The ideal would be a three speed with numerically identical 3rd gear to a five speed 5th. It would work here in flat NJ but probably not in hilly country.
SIx speeds and even five speeds are stupid consumer driven idiot inspired devices. Auto trans are similiarly going through the idiot process of more and more speeds.

I disagree. In some cases it is not necessary, but in these times when you want to eek out as much gas mileage as you can, the right gearing on a 6 speed will help tremendously.

To the Op, there is a 6 speed that fits, but If I remember the final drive might have been numerically lower, meaning it would get worse gas mileage. If you could swap the Echo's final drive in that woud be much better for gas mileage. Not sure how much that would cost though.