So my truck is a 2002 gmc with a 60e . When I get on the freeway as soon as I hit 55 it starts shifting between 3rd gear and 4th constantly. I have to step on it all the way and let off and repeat . Any ideas what it might be guys ? Tia

 

Welcome to the 4L60E.

That's called hunting, and the 4L60, 4L60E and 700R4 were all famous for it

Tune will fix that right up

 

Any tips . So I just tell my tuner to tune the tranny with his hptuners ?

 

Pretty much. Tell them its hunting and you want it to hold the gears better.

Most of the time when they tune the trans it goes away as a result of just making the trans shift better.

 

I'm not sure a tune will help much. I have had the same issue, pulled up trans live-data on scantool during test drive, and everything checked out normal EXCEPT the duty cycle of lock-up solenoid which stayed at 96% the entire time. Got trans parameters reset and then tweaked to match the mild build and shift kit the 4l60e has. Been 8 months, and symptoms have stayed the same, but the frequency of which it happens has increased over time. My next step is replacing the torque converter and the harness, since the lock-up solenoid is wired directly into it. Basically it "unlocks" every time I left off the gas, and then reapply....forcing me to stab the throttle and left off to keep it in overdrive lock-up. Can't think of what else would cause this problem....and just haven't had the motivation to pull the transmission again to replace the converter.

 

Try setting it to full lock-up in 4th.

Don't drive it like that for long, could overheat the trans or burn the converter over time.

If you have the same issues with the TC commanded to full lock-up, than you may have a TC issue.

You do realize that the TC doesnt even lock up until 44MPH right? You basically need to hit 45mph to cruise with the TC locked...and if you go past 1/2 throttle you will kick it out again.

I have attached a page from HPT with The TC table. Basically set the 4th release to 318 and the apply to like 20 in the green section. See if its in and out then.
If it is, your solenoid is toast, or your converter is toast.

You can also set up this table to make it never lock, or to have it stay locked in all gears, than click a tab to have it stay locked through shifts.


I also noticed a huge difference when I swapped out to full synthetic ATF.

 

You just described my truck we have the exact same problem