Built 6l80 slipping

[Lslatampa]

So I have a fully built 6l80 and it is slipping under wot. It?s a stage 4 Gearstar transmission. And it will also slip in 5/6 on the highway just trying to maintain speed. Could this be a hard parts issue or tuning? And could it possibly be from the 3.08 gears? Thanks in advance

[SgtlesDavenport]

Has the tcm been tuned after the install?

[Lslatampa]

Yes, it has a new tcm and has been tuned

[hjtrbo]

Check pcs 1 is rising with load. Also connect a pressure gauge to the test port and verify with the service manual. On a stock transmission the pressures you see should approximate the values below +/-125kPa...
PCS 1 pressure x 2.045 + 300

Test in the driveway first in drive and apply varying load with the brakes on. You should see an almost linear rise of line pressure to PCS 1 prressure. Eventually you will hit the pump mechanical pressure relief which is around 2000kPa on a stock trans. Be mindful of fluid temperature. This should only be a short data gathering test.

Do not keep slipping your trans. Do this test driveway first then if numbers look ok, drive once around the block from home then put it back in the shed. You'll be needing new clutches in 3 weeks if you keep driving it.

Assuming your pressure is ok, first place I'd check is the torque model is accurate on the ecm side. If you bump up air mass a this will report a higher torque to the transmission which will then cause a higher pcs 1 pressure which then obviously increases line pressure.

Been a built trans which by the way I don't have any experience with unfortunately, I have read that the clutch volume boundaries may need adjusting which is because the builder may have stacked clutches a certain way which affects the clutch piston volumes required to engage the pack.

Torque is torque, the trans will not care what diff gears you have.