..let's assume that the shop re-jetted your carb, so fuel mix isnt an issue...
..one thing that you can do, and from what you say might be the best thing right now..
..lighter rollers..
..you need to get your take-off rpm up to at least what the pipe's powerband requirements..
..usually thats somewhere around 8500..
..this will help your launch and eliminate the "shift"
..ideally, you're looking for a constant rpm thru acceleration, until you approach top speeds, then they should rise a bit more..
peace