RPM's on highway, yes I know they are usually high
 

So had my G for about two weeks. The car usually turns about 3.2k at 70 which is as expected. But, on my drive back to Jax this last week I noticed I was turning a lot more than that. About 3.5k indicated at 70 and 3.8-3.9k at 80.
The car was still indicating 22-23mpg so I know the actual RPM had not increased and the trans was not slipping or anything.

I think I read somewhere that the tach's in these cars suck and have caused issues or were inaccurate. I was going to do a ECU reset and all that good stuff when i cleaned the TB's this weekend to see if that made an impact.
I also saw someone replaced a capacitor on the gauge cluster that was causing issues so i might take that apart as well and check it out.

If anyone else has had this issue please let me know your thoughts. I couldn't find any threads with this specific issue.

Plug in an OBD2 scanner and compare the data being sent for RPM to what's actually being displayed. This will get you pointed in the right direction because if the ECU is displaying the same RPM as the tach then you might be experiencing early failure of a crank position sensor that the tach gets it's data from.

Also, those rpm readings are SUPER high, my 6MT pulls about 3k at 80mph and the 5AT should be like 500 rpm lower than a 6MT. Are you SURE you don't have tranny slippage because that's usually how it happens in an automatic transmission, rpms start to climb and eventually get higher and higher until the clutch plates or brake sleeves are completely worn off then it just free-revs while in gear if you lost a high gear clutch pack, it feels like a CVT if you lost a brake sleeve, otherwise you get a turbine revolution error code if it's a lower gear clutch pack.

Higher gears are more prone to this type of wear because they have to move the vehicle without the assistance of gear reduction on the lower gears.

You didn't say if you had an X, or a manuel tranny, on my 07 X it turns over at approx., 3 grand at 70 mph, 3800 or 3900 seems a bit high, for 80 mph, ( but my car runs so good I don't pay any attention to that) in top gear, the mpg is not a good gauge of any drivetrain quirks.... anyway, there should NEVER be any diff in rpm's at any given speed, ( with a manual) and unless ur towing, not much diff with the 5 speed auto either....

Whoops, didn't see which subsection this was, didn't realize you have an HR equipped sedan. Yeah your FD is 3.7 so I have no idea what your cruising rpm should be.

Ok, here's the math on where you should be at for cruising rpm.

https://cimg0.ibsrv.net/gimg/g35driv...25f5b3808b.jpg

Either way the ECU will output the correct data being observed from the CKP, the only difference in the HR equipped vehicles is instead of the signal being directly received by the instrument cluster via CAN it goes through the AC control amp first.

If the tach jumps around but you can't tell a difference in rpm it's probably a failing stepper motor on the instrument cluster unfortunately, definitely troubleshoot though by checking the rpm with the OBD2 scanner when you get it.

That's good, the instrument cluster isn't exactly cheap. Do you think maybe you had it in manumatic mode and were in 4th gear? That would make a lot of sense since that puts your rpms at about 4k.

I read this thread a couple of days ago and tried to make note of different RPMs at different speeds. The only one I remember was 80mph and around 3250 rpm (using the tachometer so that value is 'fuzzy', sorry). According to that calculator above, it shows 3118 rpm so I call it "close enough". I'm going to double-check the input values to make sure they match my car now....