It hesitats when it's warmed up

You replaced the catalytic converters -- that's a pretty serious expense to take on, for it to not solve the concern. Engine performance issues such as this require hands on testing using proper diagnostic equipment (General Motors "Tech II" diagnostic tool or equivalent), and reference materials (workshop manual, wiring diagrams). You have a fuel delivery, engine compression, engine timing, ignition spark, air intake, emission controls or exhaust flow concern that needs to be found out. www.repairpal.com/repair-shops - check that link to find some shops near you that can help.