Locating the correct tire diameter and revs per mile?

New tire time. Probably going to be the last new set on my 15 year old truck. I'm still trying to figure out what the correct tire diameter is supposed to be. Bear with me, I'm over thinking this...

Stickers on the door jamb say 265/70R16. Sadly, this size makes my speedometer run 5-10% too fast, so I switched to 265/75R16 tires and now the speedo agrees almost 100% with 2 different GPS units. The difference, if my calcs are correct, is roughly 21 revolutions per mile using a 31.65" diameter tire instead of the stock 30.61" diameter tire. Is there any way to get the factory specs for revolutions per mile that the speedo is looking for?

While the wider tires look fantastic, I'm sure I'm suffering from added weight, rolling resistance, and loss of winter traction. I think I want to take a look at 235/85R16 tires which should only be about 2 revs per mile off from where I am now.

Thoughts? Words of wisdom?
Thanks!!!

 

This may help.
https://www.tacomaworld.com/tirecalc?tires=265-70r16-255-100r16

 

Stock tire size is 265/70/16 (~31"), but my speedo is also more accurate with 265/75/16's... it was just off a bit from the factory, and this is normal.

You can go to 235/85/16, but these are only offered in load range E so they'll be heavier, and this will likely cancel out any potential gains from the narrower tire.

I'd either stick with 265/75/16 for speedo/odometer accuracy, or go with 265/70/16 for better mpg and live with it being a few mph off.