1999 Dodge Durango 5.9L 4x4 OBD2 Codes P0740 & P0420: Vibration, Gear Shift Issues and Exhaust Leak Concerns

My 1999 Dodge Durango with a 5.9L V8 engine and 4x4 drivetrain has recently started showing OBD2 diagnostic codes P0740 and P0420. The truck begins vibrating suddenly, which stops immediately when I release the accelerator—then returns normally as if nothing happened. Notably, the check engine light turns on whenever the vibration ceases. I've connected an OBD2 scanner, and sometimes only P0420 appears, while other times both codes are present. The overdrive function still works, but occasionally, the transmission fails to shift properly—feeling like a single gear when I floor it (this happens intermittently). Additionally, I’ve noticed that 2nd and 3rd gear shifts feel harsh and sometimes occur too early. I understand that P0420 relates to catalytic converter efficiency. I've already inspected the exhaust system and found an exhaust leak—could this trigger both P0740 and P0420? While I know P0740 is a transmission-related code, there are many potential causes, so I'm looking for help narrowing down the root cause. I don’t have funds to guess or replace parts blindly. Any technical advice, troubleshooting steps, or explanations of how an exhaust leak might affect these codes would be greatly appreciated.