Will not accelerate after replacing the alternator?

18 volts is too high. can I ask which brand you used for the rebuilt alternator? I would use a Denso unit. Also lets run the codes to see what comes up.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

and

https://www.2carpros.com/articles/engine-has-low-power-output

Let us know what happens and please upload pictures or videos of the problem.