Re-gear, new problems

Hey, I've got a 2020 Tacoma 4x4 Offroad. I've put a 3" lift with 285's. Last year I had the dealer download a upgrade software to help with sluggish response. I'm sure most have experienced this. It help a little and seamed to improve shifting. but not enough. I decided to get it re-geared and went with 4:88 upgrade. Thought this would help with millage as well as torque. It actually does stay in the upper gears on the hwy. BUT here's my problem... 1) gas mileage went down considerably. 2) when I'm going down steep hills it will down shift on its on. To the extent it will push my rpm's up above 4K. I have to go into manual and up shift to get to the right gear for the speed I'm doing. Is there a way to fix this?

 

It’s hard to propose any theories about your gas mileage without more information. Changing your diff gears could cause your fuel economy to go up, down, or stay the same.

Your description of the transmission behavior doesn’t add up. I’ve never had an automatic transmission downshift while going downhill and maintaining my speed. I’ve also never observed s-mode forcing an up shift. S-mode simply limits the top gear the transmission will use and is designed for engine braking.

 

KDMax time

https://www.tacomaworld.com/threads/kdmax-pro-tune-by-paparee-and-twtaco.713699/

 

What were your expectations going into it?

 

Don't be too sure, I've got 5.29's and the KDMax tune and I get the same downshift when going down certain steep hills after applying minimal brake. I have to go to S mode and up shift on one hill every time I slow below 50 mph.

 

The truck is designed and programmed for engine braking, which downshifting transmission happens. As for poor gas mileage, you went to 285's and 488's it going to take a big hit in gas mileage.

 

Go back to stock gears and get the ott tune

 

I would think your mileage went seriously down with the 33" tires you added. Just wondering, did you measure the actual mileage between truck changes?

 

Bigger tires = more rotational force needed to spin them.... gets worse the faster you go. More gas needed. This is physics.

In all your gearing and tires, did you get your speedo adjusted? Usually the same input is used for calculation of mileage.

My tires near doubled in weight from stock 32lbs to 63lbs..... mpgs dropped from 23ish to 17ish.

 

I'm running 64lbs a tire add my method wheels 25.4lbs comes to 89.4 lbs a corner.