Speedo gears interchangeability

[TurboMax]

I just swapped out the 3.909 ring gear & pinion with a 3.54 setup to improve my mileage. I'm currently running a 5-speed with stock 14" tires. Do I need to also swap out the speedo gear? If so, which speedo gear? I believe the stock 5-speed truck uses a 23 tooth speedo gear.

[Rahtid]

have you noticed any difference mileage

[TurboMax]

It went up about 2 mpg mostly street driving. I'm pretty sure that you can get a couple more mpg in hwy mileage. rpm's drop from 3200 to 2800 going 65-70 mph. Still need to find a 21 or 22 tooth speedogear though. I just have to remember the speedo is off 5mph.