I have a 2004 chevy tahoe I need to replace the engine can I swap for a 5.3 in doing so will I have to have to change out the computers

you didn't tell us what you have now. If the donor motor is identical you won't have to reprogram the engine computer. If it's close (but no cigar) you may be able to keep ECU but reflash it to a different factory spec to match donor motor (you generally can only reflash to factory specs). If it's a different motor (later or earlier generation intake, different tranny controller, etc.) then you you will have to swap out everything including computer.

Keep in mind that to be smog legal the motor must be the current year or newer. Check with your DMV for details!