I think your charger might be the problem. I personally had a 16x3 myself, and it did it's job of charging the battery, but for the panasonic cells, the 16x3 does not offer adjustable delta mv needed for the panasonic. Since the charger charged your Sanyo with no problem, then I'm assuming the delta mv is set higher than 3, which is too high for the panasonics.
Try a charger (if that's an option) like 16x5 and up (16x7, 16x9) I personally use a 16x9 now and it has been charging my 3000s without a problem. Also, a buddy of mine that works at Novak suggest charging the panasonics at no higher than 5 amp, and to put them on a tray for about 1 min. before charging (this will equalize all the cell before charging).
One last thing, I personally find that the panasonics are great once a week racing packs, they tend to feel flat on back to back runs (same day, or consecutive days of running). The Sanyos seems to be okay with back to back, but the panasonics, especially the UMH are ideal for one week run.
Hope that helped
Speed Tech R/C