I'm not sure how to tell, but I don't think my truck with this converter has ever locked until 4th gear when doing a 1/4 mile run, even before twins. I haven't been able to tell, but the rpms after the shifts on 2-3 never drop below 3400 rpms or so. Only going into 4th does it drop down to 2500 rpms as well as into fifth. Then again I haven't figured out the gear ratios, but it sure doesn't look like mine has ever locked before 4th gear at wot during a 1/4 mile run.
Jody