I have 2015 f150 3.5 eco with 6R80 and 32" tires.
I just installed True Trac LSD with 4.56 gears. my pattern is pretty spot on and all new bearings. I marked my driveshaft and installed it back to where it was.
Since doing so the truck goes to 6th gear before I even leave 35mph. I try to push it longer and when going around 60 I hear a loud hum that gets louder with speed. I am unsure whether it's coming from the transmission or the rear end. when it's on jack stands and I rotate the tires there's no audible sounds from either. I am in the process of buying 35" tires. could the 32s be making the trans shift so fast and be making all the noise?

 

Did you adjust gear ratio in ecu? Shifting is based on output shaft speed and yours is now spinning faster at lower speed and shifting earlier.

 

I have a sct tuner from brew city boost that allows me to change the gear ratio. I assume that it would've done that for me but I suppose I should look into that, thankyou for that tip

 

I regeared my 2016 5.0 Screw with 295/60R20 (~32.5" actual height) to 4.56 last summer and as for the early shift points, yeah that happens when you re-gear that low. The only way around that and have the transmission hold the gears longer is going with a custom tune, probably from 5 star because I know that their daily driver Perf/Tow tunes hold the gears longer than stock; at least it does on my 5.0. Not sure about the Ecoboost.

The shift points are based off of output shaft speed, not vehicle mph. So after re-gearing to 4.56, the truck will upshift at lower vehicle speeds, keeping your engine rpm low on the stock tune (as well as most custom tunes - in my experience, most other custom tunes will have shift points similar to stock). In other words, the engine computer on the stock tune will compensate for the extra engine rpm the 4.56 gears force, so the transmission will upshift quicker to try to keep the engine rpm in the same ranges as with your 3.55 gears, or 3.31, whatever the truck had originally.

As for the noise, I'm not sure about a humming sound, however, I know that most aftermarket gears have a slight noise associated with them, but usually its is more of a whine than a humming noise, so I can't comment on that.

 

you should be able to input gear ratio and tire size.

 

So do you think from 40 to 70 mph and holding 70 for highway is OK? I want to say it stayed steady around 2500rpm at 70

 

no comprende

 

oh sorry I left out one key thing. it's in 6th gear from 40 mph and on. do you think that is OK even if I ride that to 70-75mph on the highway and holding that speed for awhile

 

The PCM calculates the NV ratio, which is basically the tire RPM vs the engine RPM when the transmission is in a 1:1 gear ratio. This NV ratio is affected by both tire size and gears.

You may want to consider reflashing the PCM back to stock and then reflash again back to your BCB tune with the correct tire size and gear ratios to see if you can get the PCM to initialize the NV ratio calculation. This NV ratio calc should correct for the ratios and stuff.

 

40mph doesnt seem that low. My stock tune truck will shift to 6th around 45 mph with 3.73's.