About parachute yes i know but it is not same as the original however it is not a big problem though but taxi wallclimb has no alternative.
In vice city and san andreas if you complete taxi missions you will be able to boost your taxi with horn download a 100% save file get in a taxi and press horn button you will see what i mean.
With getting right angle with taxi in walls gets you a huge boost example from vice city;
This also happens in san andreas here is example
This is a method of stunting and it doesnt work in mta sa hope developers add this feature from the game