Only under acceleration, uphill, or under load, basically a gentle sustained second gear pull, a slip, what happens is a high rev, then, gear engages, second to third, solid. Modulator?
You can try and put a 'shift improver additive' but don't bet on it, that it will work.
I've also heard if you have a worn tranny and you do a tranny flush and refill of fluid, you'll damage it more because the old fluid has the the old dabree that's barley making it shift.