Ditch the split shots, weight the fly.
Doing your Bill Dance impression?
I don't use split shot, and the nymphs I use are all weighted. The only time I lose fish is when I use a size 18 BHPT which I rectified by tying them on size 14 scud hooks.
I suggest next time that you start with the smaller fish further down stream so as not to alert the bigger fish. That should get you settled down enough to hook/play the big boys to good affect.
Jim