What doesn't go smoothly exactly? Are you not able to hold the slide once you get it going or are you having trouble releasing the fins to go into the slide? With big fins, it is harder to get the board to release, but once you're sideways with proper weight distribution (and handle positioning) you should be able to hold on. I used to do slides with HUGE fins (2.8) on my 99 shifty, so even tough big fins make it harder, everything is possible with proper technique.
For some reason, I always found reverse sideslides (with you back facing the boat) were easier to hold for a long time, you might want to give that a try. As for removing your fins, it will definitely make all surface tricks easier, and most people say it will help you work on your edging technique, but at some point you'll have to put them back, I don't think this board is meant to be rode finless.