When I go down hill in the TL, it seems to roughly automatically downshift once...

Like it would jerk the car a bit when going from 45 to 30mph downhill without stepping gas. (you can feel the rough downshift)

This occur before I replaced my tranny, but with the new tranny, it still occur so I was wondering if this is normal?

 

Normal. The TL has Grade Logic Control, and will downshift to help slow the down the vehicle. It's always exciting when people are in the car and you slow down, the trans downshifts and the passengers think you're a bumbling idiot that doesn't know how to use the brakes as everyone lurches forward.

 

Replacing the 3rd and 4th gear sensors fixed this issue with mine. It's likely they caused the initial trans failure in the first place. I would get these replaced asap to make sure the new trans lives a long life.

 

This might help:

ACURA
Automatic Transmission Downshifts While Descending
Customer's concern: "I was going down a hill, and when I applied the brake pedal, I noticed that the engine noise increased and the car slowed down quicker than I expected it to."

What's happening and why: The transmission's grade logic control system comes into play when you descend or ascend a sloping road ( a "grade") or when you reduce speed. The onboard computer compares memorized driving conditions with your actual driving conditions, based on various signals from the vehicle's sensors, and then uses grade logic to shift the automatic transmission accordingly.

Grade logic uses "descending control" to downshift the transmission during descent and braking. When you're driving downhill with the transmission in high gear (4th or 5th) and you brake even slightly, the computer directs the transmission to downshift to the next lowest gear (3rd or 4th). The downshift allows "engine braking" to help slow down the vehicle. Sometimes, this normal characteristic engine braking effect could be perceived as a harsh, unexpected downshift.

What can be done: Test-drive a similar vehicle (same model and year) and duplicate the driving conditions to compare the downshift speeds and the shift quality. The comparison should confirm that the downshifting of your vehicle is indeed a normal characteristic of an automatic transmission that has grade logic.

Further explanation: When you're going uphill, grade logic uses "ascending control" to keep the transmission in lower gears and eliminate frequent or excessive upshifts and downshifts. Sometimes this normal characteristic effect might be perceived as the transmission not upshifting normally. In this case, grade logic is, in fact, intended to help the vehicle run smoothly and have more power when needed.

One more driving condition could create an effect of the grade logic control system that you may notice. When the vehicle goes around a corner and needs to decelerate first and then accelerate, the onboard computer directs "deceleration control" to reduce the number of times the transmission shifts. For example, as you reduce vehicle speed, the computer directs the transmission to shift from 4th gear to 2nd gear earlier than normal to cope with the upcoming acceleration.

Seems perfectly normal to me.

 

I actually count on that in my Pilot. It's pretty predictable, even though sometimes while braking downhill will be a bit abrupt.

It has allowed me to continue on the original pads approaching 80K miles.

 

Mine does this pretty abruptly going downhill right at 40mph. Are the sensors accessible without removing the transmission. Any part numbers/cost?

 

The sensors are on the front of the trans......shifting should NOT BE jerky or slamming into lower gear. shifting would be more noticable going down hill since the entire weight of the car is being absorbed by the shift