Tin Lead plating

We are having difficulty plating Tin Lead consistantly. This is a rack process and the parts are various sizes all the parts are circular and have blind holes anywhere from 1/4" to 1" in diameter. Our problem is mostly throw of the bath into the blind holes. We just started using the Tin Lead bath almost a year ago and its been a constent battle.

Process

Cleaner( Periodic cleaner) - rinse -Heated HCL - Nickel strike- Nickel plate - Copper - Tin/lead - Dry

The Tin/Lead bath is a sulfonic acid  bath

Any help would be appreciated and if you need more info I can provide it.

Thanks

Mike