Ford expedition 2006 transmission problem?

I own a garage, and I got stuck in this thing really annoying!
Car had a problem in the 2nd shift, trans was overhauled and all parts where changed, also the valve body, solenoid pack and all.
the problem in details is, in second and fifth gear, the car when driven normaly on a stable speed shifts normally and smoothly. But when there's a kickdown the second gear get stuck and rpm goes high then I get the transmission symbol on the cluster, that's where I turn off the car and back on to test drive it again, I face the same problem then I press the gas then release to get lower or higher shiftings. Something weird I found while transmission was in rebuilt process is the band it was burned, … But what may cause this problem, is it the servo or is it a leak in the container/gear container, or perhaps piston or governor driven somehow its not pressuring well,?!

Please i'm stuck in this I have observed everything closely, what am I missing there, Please advice and help me!

A band burns because of insufficient pressure to hold it firmly, so it slips and heats up.
It is not easy to tell.
For example, if one uses a cloth rag to wipe the dipstick, that can get enough lint in to ruin a ball bearing seal, and cause slippage.
Automatics are that sensitive.

Get rid of that POS and buy a japanese car