It is either the motor or the window jamb has an issue.
Pretty common to have window motors fail as a general rule.
Does it go down smooth and at normal speed???
If so, I'd do some looking into it before I hap haggardly buy a motor. Could be a wire issue, relay or things like that if your motor is good.
Wire issue translates down to an amperage issue. It would be like trying to start your vehicle with 8 guage wire running from your battery to your starter. It is still getting 12 volts but not the amps to operate the starting motor.