I've got a '96 Ltd 4Runner with 3.4 auto which behaves a little oddly on hills.

I'm running larger than stock tires (can't remember for sure I think they are 265/75 R16 or something like that).

My problem is at highway speeds (60-70mph) in cruise control

Transmission will kick down normally as I go up a hill (shifts down normally where it should), but as I crest the hill, the transmission will hold the gear and not shift up again. If I disable the cruise and lift off the throttle, it will upshift, but if I simply try to maintain speed, it doesn't want to shift up. I've never let it run very long (more than 15-20 seconds) in the lower gear when it does this, so I really don't know if it will eventually shift up on its own. It sure doesn't seem like it.

I noticed this issue early in the new year, but wrote it off as a quirk with running the larger tires (bought the truck this way in November.)

I found someone else with a similar problem when searching forum, but no answers posted as to what was found.

Legitimate problem, or am I finding problems which aren't there?

I've got no codes or any other indications about something being wrong.

Can anyone shed some light on this problem?

 

Just wanted to add that this seems to be a problem only when it downshifts to 3rd versus torque converter unlocking. When I go up smaller hills, the truck locks and unlocks as it needs to, and behaves normally.

 

these trucks are slow and underpowered for highway use, mine does the same thing when i go up a long hill, try turning overdrive off and see if that helps you keep from shifting so much

 

also if you have ect on, it will down shift sooner and hold 3rd longer.
I've also found that the cruise on this thing is less than intelligent. I find that, as I approach a hill, if I give it some throttle a bit sooner than the cruise does, I will usually take the hill without a down shift.

 

ECT was in normal mode when this occurred, not power.....

 

I had the same thing happening when I had 265/75R16 tires.
I am back to stock tire size (265/70/R16) and all ?shifting? problems are gone.
I can even tow my boat (around 3000 Lbs) and maintain 70-75 mph going up hill :-).
Also, want to add, that problem is not just a size of the tires, it is a combination of things:

1) Rolling resistance of the larger tires, especially if you have LT tires (they have of the different combination of rubber compound and stiffens of the sidewall, than "P" rated tires).
2) Axel ratio in your truck (especially if you have 4.10, as I do).
3) And of course the power of 3.4L engine, that you particular engine has.

Just my $.02.