Good day mga bossing!

I have a BIG problem with my A/T Mitsubushi Galant 91' model and I am really really getting frustrated with it.

Everytime na mag speedup ako at around 100kp/h up then bigla ako mag stop (ex:bec of toll gate or malapit na mag exit) then bigla ko nlng mararamdaman na mag shift sya sa 3rd gear (i mean talagang ramdam n ramdam ko ang pag shift.. i think this is very unusual) then pag fully stop na tapos pag andarko ulit mag stuck n sya sa 1st gear. hindi na sya mag shift to next gear. What i do is irerestart ko ung engine then back to normal na ulit. Basta everytime na lumagpas sa 80kp/h ung speed ko ganun n lagi ang nangyayari.. then yesterday it even get worst, im driving at around 80kp/h then nag slow down lng ako ng konti ayun same problem appears..

Nagpa change ATF na din ako but hindi natanggal ang problem..

please help! saan ko kya pwedeng ipagawa or ipa check kasi d ko tlga alam kung anu na ang gagawin.

help please!

Thanks