Is it hard on the transmission to coast in neutral and then putting it into drive to increase speed to save gas? I do it all the time.
This has minimal effect on the transmission. As long as you are not giving it gas while you switch into drive you should be ok. When the transmission is in neutral, there is no effective gear selected, so it should be ok. When you put it back into drive, it will select the appropriate gear (minor and normal wear at that point).