hello howdy?

ok i'm gonna explain my situation
i have 04 accord exl 4cyl automatic transmission. it has 82xxx miles on it.
abt couple of weeks ago, i turned on engine and i was trying to move
gear shift from P to D but it didnt move. i was like "what da.....?"
so i pushed overdrive button which right next to gear shift (and i'm still doing this action whenever trying to move my car... EVERY SINGLE TIME!)
and while i was driving, the gear doesn't shift up properly. Mostly from 3rd gear to 4th gear it takes too long and needs high rpm to shift up( sometimes it happens from 2nd gear to 3rd gear) and it still going on. SO, i brought to dealership for check up. after they did diagnostic on my car, they told
me that my car has a two problem first one was ECU failure second one was
transmission problem which cost A LOT to me. They told that i need to replace new ECU and new transmission. Of course i didnt fix it
i just brought it back to home.
Two weeks ago, i took out ECU unit from my car nd sent to SIA company (expert of ECU fixing) nd yesterday i just got it from them. the estimate says "no problem found during the proceedure."
i was like "Okay..........hmm....." so i putted it back to my car. it works like
what it was but still has a problem like i said, shift doesn't move from P to D
and shift doesn't go up properly while i'm driving. PLEASE HELP ME OUT!
what causes this problem? i already checked stop light and its working.
no engien check lights, no blink on gear status lights. nothing on instrument cluster!
PLEASE HELP ME!
oh! one more thing! when almost stop my car, like under 10mph, the gear
just drop it that i can feel the shock.