Originally Posted by
Lovegasoline
...If I commit to another sport it will be paragliding.
...the groceries ought to be pretty easy to carry home that way.

It's all downhill.
So just to make certain I wasn't missing something because I hadn't ridden it for a while (it has fenders, so does not get used in the rainless summers here), I got out the Motobecane GT for this morning's Tour de Almond Croissant.
I am happy to report that it was a great trip, and I was making all the lights, just like I do on my more aggressive stuff like Raleigh Pro's and Italian Faggin's. It's a little slower to accelerate, because I put crappy Forte tyres on it with a max inflation of 95 psi. So a wee tad more of rolling resistance. But otherwise a pleasant, responsive, neutral handling, sport touring bike from butted tubing that has a good review from the frame materials nerds.
If you only weigh 135 pounds, my weight at 220 still exceeds you and 40 pounds of groceries. And my bike did not, nor has it ever, ghost shifted. Including when I intentionally climbed a couple of short ascents to get over a railroad overpass by standing out of the saddle.
So I don't really know what was wrong with your bike, but my instinct is to say that either it was poorly maintained, or set up with crappy tyres and wheels when you got it. Certainly a brake shoe lightly dragging can make a bike feel slow and heavy, as can whatever add on's like racks, a New York quality lock, and an assortment of stuff that sometimes gets added to panniers and never comes out. Anyway, if you can find something that feels quicker and lighter to you and will still do your grocer run without self destructing, you should get it.