6 speed automatic transmission?

2015 tacoma double cab trd off road 4.0 automatic.
Wondering if there were any 6 speed automatic transmissions put in the 2015. All that I have seen so far says no but I have been leaving it in 4 when around town. Recently put 285 70 17s on and was on the hwy in drive. Noticed when coming to a hill it would drop and go from 2grand to 2.5grand. I put it back in 4 and I climbed close to 2.9. In drive it seems to have 2 gears. Looking for answers. Thank you in advance.

 

There are only 5 speed autos in the 2nd gens. 4th is 1:1 and 5th is an overdrive.
Sometimes the engine will increase rpm without shifting, like going up a slight hill. Then if need be or you manually do it, it’ll shift into a gear lower.

 

The extra "gear" your feeling is the torque converter locking and unlocking.

 

Then why the rpm change. On cruise up a slight grade stays at 2 and larger hill 2.5. Think the torque converter is already in a state of lock.

 

It will unlock on steep hills or under hard acceleration to allow the engine RPMs to climb more into the power band, cruising and light loads it will stay locked to increase efficiency and decrease heat in the transmission. When it locks it's essentially like engaging the clutch on a manual transmission.

 

In other words, you're in 5th and with the torque converter locked, the engine is solidly connected to the transmission like Dm93 said.
When you're in 5th and the torque converter unlocks, there is slip. The engine and transmission aren't solidly connected and instead are connected by a fluid coupling (the torque converter). You also get some torque multiplication, as well as heat, as this occurs.

 

The locking function isnt meant to be used like a regular clutch (with a lot of clamping force). Its main purpose is to help keep temps down inside the trans by allowing the fluid coupling to rest at cruising speeds

 

manual swap

 

Those tires are about 7% taller than what came on the truck. Everything is about 7% different than what the computer is expecting. In effect your factory 3.73 gears are now about 3.49 gears. When your speedometer says you're at 70, you're actually at about 75 mph. When your odometer says you drove 200 miles, you actually drove 214 miles. That engine develops max torque at around 3600 rpm. The lift is causing the truck to catch more air.

All of that combined means your engine is working harder and needs to keep the rpm's up in order to have enough power. Dropping to lower gears, or unlocking the torque converter keeps engine speed up. And since you're driving faster than you think you are that only makes things worse. Re gearing to about 4.10 would get you back closer to factory specs if you run that size tire.

A manual is no advantage. Yes you can select the proper gear to match conditions better than the automatic transmission will. But there is no law that says you can't also select the best gear manually with an automatic. You're already doing that around town. You're going to have to anticipate that the engine is going to struggle getting up inclines in overdrive and manually downshift to 4th gear BEFORE the engine starts to struggle. Exactly the same as you would if you had a manual. Shift back to OD when you level out or start down.

It doesn't hurt a thing. In fact it is easier on both the engine and transmission. When we travel through the Rockies I never use OD. Keep the truck in 4th gear, (or lower) the entire time I spent in Colorado last trip.