kontin,
A true "80 Volt-Amp" Lionel CW-80,* of either version, will deliver 5 amperes. If each of the motors on the GG1 in question draws less than 2.5 amps, the CW-80 should have enough power, assuming that long trains, illuminated passenger cars and particularly lamps on the layout don't overload it. The green light will tell you whether the transformer is "happy" with its load. That said, many folks would want to have still more power in practice.
If the above does not happen, I would suspect that the loco needs lubrication or mechanical service to ensure that nothing in the works is binding or rubbing.
*As opposed to the much lower-powered look-alike "PowerMax" or "PowerMax Plus" transformers that come with many Lionel "starter" sets, which would be extremely challenged by any dual-motor locomotive, no matter how well it's tuned up.
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