I am not sure how well this will help in your case but there's multiple things that could be off, Ecu causing tranny to shift earlier, tachometer is old and reading wrong, tranny fluids. Those are the problems listed above; however, I ha a similar problem in a 92 Ford F-150, and it turned out to be a speed sensor on the transmission itself, not sure if these LS4's have them as I haven't really checked on my car yet, but that seems to be a common problem to my knowledge.

 

Its the stupid gauge that is not showing you the correct rpm. If it is drug down and kills the engine in gear you may have a transmission problem.

Or like in the above post as well.

And now you mention misfire? In your original post there is no mention of that!!!!!!

 

"Also it seems to be getting a little worse, when i accelerate swiftly, i am getting misfires around 2500-3500."

This was posted 2 days after i originally posted, trying to say its graduating into something more, etc.

 

Heres a video in my garage, i wanted sound to echo so u can hear the 1uz tick and how fast you thinks its actually revving according to the video

 

It's really hard to tell what rpm that its at by ear. The idle sounds fine. I think your tach problem is isolated from the misfire IMO. I would look into the tach checked out by a pro.

 

That engine sound is about 550 ish rpms. If someone had an oscope connected to a mic they could tell what it is for sure. My ear says for sure the TACHOMETER is reading the wrong thing.

 

UPDATE: Car still showing low idling on the tach but it's not idling that low. Still shifts at 4500rpm area at 80mph, getting the same gas mileage as always.

Not sure whats wrong but it isn't getting worse and just seems to be the tach is reading the wrong rpm signal from something.

Not worth the money to investigate and fix at this point.

 

The tach on my car is doing the same thing. Car idles great, runs great and sounds great. If I rev it to 800 in park it sounds like it's racing and when I put it in drive the car lunges. I picked up a used cluster so we will see. I have a IR device hat will read rpm's so I'll use that to check first. I have what feels like a miss only in the 55-60 mph range but my tach says 1k rpm and I know that's not right. Also my wife said she fills it up on Sunday but the needle stayed at half so the that kind of confirms the bad cluster. You've done a lot, and some of the things I have yet to do. After I check the TPS I think I'll give in and take it to a shop.

 

Let me know if the cluster fixes your issue, my gas needle is OK though.

Does yours shift around 4500 when you max out first gear in D ?

 

The tach never gets that high. The cluster I got was no good so I'm still in the same boat. I'm going to take it to a shop and let them go over it then just have my cluster rebuilt.