1998 Jeep Cherokee Check Engine Light On: Fixing P0138, P0463, and P0720 Trouble Codes

I own a 1998 Jeep Cherokee and recently had the check engine light come on. After taking it to a mechanic for an OBD II scan, three trouble codes were detected: P0138, P046-3, and P0720. The shop advised me not to worry, but my vehicle feels sluggish—especially when accelerating—and I suspect there's an underlying issue. I'm seeking clear explanations on what each code means, the necessary repairs, how to fix them, and the potential consequences if left unresolved. Can anyone confirm whether these codes indicate serious problems or if they can be safely ignored? My car is not responding well to throttle input, so I'd appreciate expert insight into next steps.