Need help figuring out top speed issue (regearing)

Because your 37s “reduced” your gear ratio.

 

This issue has been discussed many times. I believe it is due to a max speed governor that determines speed via the drive shaft rotational speed. You messed up its calibration by changing your gear ratio. The max speed is normally 115 mph, but you changed your gear ratio by 36% resulting in a max speed of 86 mph.

5.29/3.9 = 1.36
115/86 = 1.34

I think you can adjust the setting in the ECU. Use your favorite search engine. Here is one thread I found:

https://www.tacomaworld.com/threads/maxed-out-at-133kmh-83mph.730131/

 

you need someone with VF Tuner, like myself, to increase the top speed. Currently from factory top speed is 170kph. Someone with VF Tuner can increase that to 255kph. Let me know if there’s any way I can help you.

 

Probably because you were too busy focusing on those smiles you were putting on your face!

 

Hah, that is true but manual trans here so no actual governor changes for me. I’ve had it up to 100 with the gears and with both stock and 32” tires.

 

Are you implying there is no top speed governor on the trucks with the 6mt?

I’ve only had my 6mt up to just over 100 during the zombie apocalypse that left the roads unoccupied.

 

Not that there is no governor, but that the governor (if there is one) is not affected by a regear on MTs. We don't have the speed sensor in the transmission that the automatics use to measure driveline speed to use as a governor.

There could very well still be a governor monitoring the speedo on the manuals, but that method would not know the difference between a regeared truck and a stock one.

 

Interesting. I learn something every day.