random 1-2 slip when warm!

[SensRanger]

I have barely 4,000 kms on my rebuilt 4r55e and need to bring it back AGAIN. Under medium load (4 passengers, bed full of camping gear) the same thing has happened twice: After driving for about an hour, we pull over to stop for a minute, putting the trans in Park, but not shutting off the engine. Time to go, put into D, and won't shift out of 1st without letting off the gas! Things seem fine when cold, though I am getting paranoid about a 2-3 flare again, its not like before when the RPMs spiked by 300-400, but there is a 'blip' of maybe 100 RPM. Could this be normal or should the RPMs drop right off with NO blip/flare whatsoever when it shifts. Advice sought before I bring it back under the rebuild warranty! Many thanks.

 

[Glacier991]

One of the unknown factors when you get a rebuild is what, if anything, is done to the valve body. In the case of the 4R44, 4R55 and 5R55 the valve body is a definite problem child. Many shops, if the VB is not giving a problem, will simply pull it out, rebuild the tranny with a soft parts rebuild, and put the VB back on.

When you had it rebuilt what was the mileage?

Your problem sounds very much like it is VB or solenoids.

 

[BrooklynBay]

Other possibilities could be that they didn't torque the VB bolts correctly, the bands could need an adjustment, or they didn't use Mercon V. I suspect the VB gaskets, and bolts being loose, or too tight.