Hi Willie,....
Did you ever have problems with the gun when shooting percussion? Given that the same gun was shooting ok with proper timing and full ignition when using cap & ball percussion cylinder,... the problem may be with the Kirst cylinder. Try swaping the Kirst from the one that shoots ok into the "trouble gun", and see if the problem still occurs. If not, the problem is with that Kirst cylinder, in which case it may be a Kirst for Pietta Remington, instead of Uberti,...just a thought , but I'm not even sure a Pietta Kirst would fit into a Uberti Rem frame.
At any rate,...you may have to send the cylinder back to Kirst, or better yet send them your entire Remington you'd like it to function in. I'm sure they'd be happy to straighten things out.
Have you been having problems for 9 months with Kirst,.....with this one gun?