The actor, who was last seen on screen in July, told the Radio Times that Peter is "in a much better place" after spending five months in Los Angeles with girlfriend Carla Connor (played by Alison King).
However, he hinted that trouble may be in store for the couple when they return to Weatherfield this month to find Peter's ex-wife Leanne preparing to marry former husband Nick Tilsley.
Commenting on Peter's latest claims to have stopped drinking, Gascoyne said: "I do think [Peter's] changed. Being away was a good thing for him and he's in a much better place.
"He may got sucked into his old way of life now he is back in Weatherfield but at the moment he's fighting that temptation."
Gascoyne revealed that Peter and Carla have a "tempestuous" relationship and something is "not quite right between them".
"It's hard to put a finger on it, but you do get a sense that it's not quite as it should be. They're not 100% together with each other at the moment," he explained.
Peter is "shocked" to hear of Leanne's engagement, he added.
Gascoyne said: "I think he wants the best for her and wishes her well, but I think he still does have deep feelings for her and believes she has feelings for him. I think Peter doubts whether Nick is truly the person Leanne should be with.
"But it does really boil down to Peter and his ego - he cannot stand to see Leanne wanting to marry Nick Tilsley, really."
Earlier this month, it was reported that Peter is to split with Carla, leading him to try to win Leanne back.
> Chris Gascoyne returns to 'Coronation Street' set
> 'Coronation Street' Ben Price talks Nick, Leanne future - interview
> POTD: 'Coronation Street' showdown for Fiz and Kirsty
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