Hello po again! Haaayss lagi na lang may problem

Help naman po, bakit po pag narereach ko na ang 16kmp/h biglang lakas ng shifting, no problem naman po onwards. Palagi ko lng naman pong na eexperience if mareach ko 16kmp is yung auto-lock..
I tried many times from 0 reaching 16 up, and yung mag shi-shift na xa ang lakas ng feeling, biglang alog.. but after nun wala naman na po IF not going below 16kmp
Also i tried turning off the car (Gilid ng highway) then start, going to 16kmp, biglang wala naman po! Then mamaya nabalik

Okay naman po atf kakapalit lang nung January sa casa, engine support okay naman po.