I love dream whip. I've been using a version someone posted that uses boiling water instead of milk. I like this one the best, but if comes out grainy. Is their a certain order you mix things in to make it smoother and not grainy.
The only thing I can help with is that I read that sometimes if you let it sit a day the grainiess ( If anything this will get this bumped to the top for other people to see.
I use the dream whip icing a lot and I don't have a problem with it tasting grainy. Not sure how you're doing it cause I know I've seen a couple of different recipes. One where the dream whip is just added with the confectioners sugar etc. How I do it is that I add the dream whip to the boiling water along with any salt or flavourings. I just keep on wisking it with a small wisk and it gets all dissolved. HTH
I do the same thing as the PP. I add my dream whip powder along with the liquid ingredients so it has a chance to dissolve. I've never had a problem with it being grainy.