vert jumps when down speeding from 70

[Phan]

hi everyone, so here's my problem when i'm accelerating to 70 and above its fine, but when i let go of my gas pedal from around 70 it jumps and then it down speed fast. if i keep a steady hold on the gas pedal while down speeding from "70"ish it would down speed moderately. so yeah like i said when i let go of the gas pedal for 70 and not put my foot on the gas it jumps and down speed fast kinda like its losing power.