So while I am driving my g35 05 infiniti (with 188 k miles), it shifts correctly going from 1->2 then going from 2->3. Once I get to ~45 mph, the car shift and the RPM goes from 2000-2500 to > 3200 and as the speed keeps increasing to ~60 mph; the engine runs at 5000-6000 rpm without shifting. If I switch to manual shifting while at 50/60 mph; the car then shifts to 4th gear and runs normally.

Any suggestions on where I should be looking and how to start diagnosing the issue? Thank you in advance for all the help, I am trying to keep my car alive to 300k miles

 

Firstly what's your fluid level with the tranny at operating temp while the engine is running?

Since you can M3-M4 shift without issue but it's not D3-D4 shifting I'm leaning towards neglected fluid change interval. If there was actually something wrong with the solenoid or brake sleeve it would be either throwing a code or you wouldn't be able to M3-M4. Line pressure for D3-D4 probably isn't high enough due to neglect.

What was the condition of the fluid on your last drain/fill and how long ago was it?

There is a service port on the right side of the tranny for doing a line pressure test. You should have 55-62 psi at idle, 190-218 at stall speed.

If you've never done this kind of test before read up, basically you just put the car in drive, set the parking brake, push the brakes down hard while you push the gas until you're at 2750-3000 rpm (powerbraking the transmission) then quickly read how many psi is on the gauge.

You don't want to just sit on the converter though it can be absolutely destructive to the transmission internals if you do this for more than a few seconds so be quick, get your reading, and get off the throttle/converter and let it cool back down for a minute or so. It's better to have a second person read the gauge, plus the hose isn't typically very long and won't reach all the way up into the cabin. Just be sure to be safe and not put anyone in the line of fire in case your brakes fail or something. Just have them stay on the side of the car and read the gauge with a flashlight and not be UNDER the car at all obviously.

Or you can just get a gauge with an extra long hose and have it up in the cabin with you. Only downside to this is you typically have to add a little fluid back when you're done.

 

Thank you for the quick response. I bought the car used 2 years ago and had few slip issues so I did a tranny flush; which caused the tranny filter to clog so another flush had to be done. This was ~ 2 years ago. Since then I haven't replaced the transmission fluid. I was thinking of doing a partial drain.

I will try to get a pressure reading tomorrow. As for the transmission fluid level, I see it going beyond the marking and it's covering 1/4 of the stick.

So you don't think it's an issue with TCM? As reading through and some friends told me that this might be the issue

 

Make sure you checking the fluid level correctly. Car should be at operating temp, parked on level ground, with the engine idling to check fluid level. It sounds like you are overfilled by your description of the dipstick...
What transmission fluid are you using? Start with a drain and fill, it should take about 4 qts.

I'd recommend adding a magnefine filter to your transmission cooler lines, since the trans only has a mesh screen.

 

There's pretty much no way you could have clogged the filter on this transmission, it's not even a real filter just a large sediment screen.
You could always take the car to Nissan for a 1 hour diagnostic.

 

Thanks all!!! I will take the car to the infiniti dealer tomorrow for a preliminary diagnosing and will update the thread

 

Here's the update. I took the car to the dealership to do the diagnosis and they didn't find any codes so that pretty much rules out the TCM and the valve body. They think it's more of a mechanical issue; however, it shifts correctly in manual so...
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I also discovered that if I am accelerating really fast, then the car seem to be shifting correctly. Will try to do the partial drain/replenish of the transmission fluid; just need to find the right pump size for this. Feel free to provide any additional suggestions or things to look for