I'm almost certain that premier does not "tween" frames it merely repeats them for slo-mo. If your not slowing things down too much premier will yield satisfactory results. If you want really slow slo-mo or a speed ramp effect then twixtor is the way to go, although it's fiddly to use and expensive. If youv got money to spend consider getting a compositor such as Combustion which has a slowmotion tweener far better than plug-in software and tons more to boot (colour correction, particle systems, keying, titles, 3d compositing, tracking etc etc yadayadayada)

tonga