4R75E from a stop and only in D transmission acts like it hits neutral at almost wot

08 King Ranch with a supercharger, freshly rebuilt 4R75E with many updates and a moderate shift kit. From a dig in D (does not do this when shifting manually into 1st) transmission acts like it goes into neutral momentarily, then tries to engage when at high rpm's then disengage and engage. You can imagine what it sounds like (rev, whistle, slam, squeal then repeat until you let off the throttle). Not sure what is making this happen but it didn't start until I got the built transmission back from the shop.

I have the supercharger 93 tune where I like it but the transmission is about 99% complete. Just need to get rid of the neutral type flair in drive from a stop light. I need to get some confidence behind the transmission before I can let the wife take the kids get groceries with my rig.

Attached is my current tune: Attachment 59333

93 octane supercharger tune: shreds the tires while accelerating in first, chirps 2nd gear and continues to pull hard, third gear kicks like a mule but no chirp. Fuel shut down at 99 mph. (It's a 6000 lb full sized four door truck).

Thanks ahead of time for anyone that can answer or help me fix the D flare.

Sounds like it's slipping really bad. Check your fluid levels. If they are good I would look into torque converter or maybe it's faulty rebuild.

It sounds like either the forward clutch wasn't installed correctly, either a lip seal or clearances or the one way roller clutch could be bad. With the symptoms provided, the one way roller (low) is more probable in this scenario, as the manual 1st forces the low/reverse band on and acts as another holding member, effectively assisting the one way roller along with giving engine braking ability. In either case, the trans needs to come back out.

thank you for the input. i will contact the builder this week.

In the process of wreaking stuff. I have a transmission malfunction and O/D flashing on my cluster. After the trans was rebuilt for the 5th time then installed I still have the transmission malfunction fault and O/D light flashing. Took it to the dealership to have it scanned. Shows two problem codes. One P0960, PCA or LPC solenoid Open Circut. Line pressure solenoid valve current. PCA Harness wiring, PCM inspect connectors for signs of damage, water ingress, corrosion, etc. And the other one is P0748, Line Pressure COntrol Electrical Malfunction. She kicks like a mule into all gears. Trans has new valve body and solenoids from Sonax (sp). Any help? Thanks,

I have had a few of those trucks and E vans here at the dealer that have had a failed EPC (Line Pressure) solenoid driver go bad in the PCM. It's hard to catch in the act with the DVOM back-probed into the LPC circuit, but I have had it bite me. Took two rebuilds to finally figure it out as it came in the door with burned directs and forwards, benched and overhauled, slipped like you described, benched and rebuilt again, caught it before it did major damage the last time in.

I ended up catching it in the act with the DVOM back probed to the PCM and it was not commanding the correct line pressure solenoid voltage on the output pin, but was doing so on the scan tool side.

Also, those trucks have an issue with wire chaffing on the trans harness. Usually rubs through or burns through by the RH manifold, when the engine torques under throttle it rubbs, grounding whatever circuit has rubbed through, in the EPC's case, that causes low line pressure. I'd really be looking at that harness before suspecting PCM in this case.

Either way, if it's been operated too long/much, it will require another trans teardown as well unfortunately.....