I have a 1999 Eldorado which was experiencing Fuel Pump Pressure and Level Sensor Problems. As a result, I was getting DTC codes for Bank1/2 Too Lean. I replace the Fuel Pressure Sensor and had the dealership replace the Fuel Pump and level Sensor. My "Too Lean" problem seems now to be gone but have been replace by two DTC codes. P0741 TC Performance or Off and P0440 Evap System Failure. Prior to having the Fuel Pump replaced, I never got either of these codes. When the P0741 code is set, the car still drives fine and uses overdrive. Of couse, the dealership insists they have nothing to do with the Fuel Pump changeout, the tranny needs work and it's merely coincidence that it happened the very day I got the car back for the fuel pump change.

Could these codes be a false codes set by some other issue?

The P0741 may be just coincidence.
But the P0440 may be caused by a poor install of the tank pump/sending unit. If you smell fumes well after the tank has been filled, the main O-ring may be out of place or damaged. Otherwise, a line may be loose, etc.
Ultimately, you may find that even this code is also coincidence.
Older, high-mileage vehicles tend to require close scrutiny when doing repairs, as experience has taught.

The 440 code is sometimes caused by the gas cap not fitting securely or the "o" ring on it is damaged. Could be due to a sloppy fuel pump install like Capt. Rich said earlier.

Got my Eldorado back and the Evap Failure has been fixed. Dealer left behind loose hose fittings to the canister when replacing the fuel pump. I made sure all codes were cleared and drove again. DTC P0741 remains. Still seem too coincidental to me. Is it possible something else external to the transmission could cause this?

P0741 deals with internal transmission torque converter slip.
A proper scan tool that is capable of reading the sensor's data inside the transmission would show the slipping torque converter and the fluid temperature.
It is critical to know exactly what conditions are present when the code stores.
GM Technnical Service Bulletin (TSB) No. 08-07-30-025 from May 2008 addresses the diagnosis for this. After thorough diagnosis can you determine if an updated converter is needed.