The straight-through drive from St. John's to Deer Lake (just east of Gros Morne) is about 12 hours nonstop. We spent a week in just Gros Morne once, so your 1 1/2 days is not enough. Newfoundland is big.
You could fly from St. John's to Deer Lake, about 1.5 hour flight.
If you can't stay longer than a day or so, you can drive to Cape St. Mary's bird sanctuary, about 2.5 hours each way. The peninsula just north of St. John's up to Flat Rock makes for a nice hour or two's drive, and the same is true for the ride south of St. John's. At this time of year, you might be lucky with icebergs in the St. John's area.
Or, driving a little farther, you can go over to the Bonavista Peninsula, lots of historic interest, beautiful land and sea scapes, and better chance of icebergs up on the northern tip. The Bonavista trip will take an entire day, minimum.
Also, if you've never been to St. John's, you could spend the entire time there, no problem, a very interesting walking city, photographically and otherwise.
We've been to Newfoundland twice now, 2 weeks the first time, about 10 days the second time. Didn't even scratch the surface.