Hello again,
I don't want to take up anymore of your time as I have a way forward with jpegs for slides. But, I thought I would share with you some further info. Below is a shareable link. In it, contains 1 gif, a v6.22 project & a v7.3 project. I also have a PDF with screen shots. When I drop the gif into v6.22 it takes on the default duration of 5 seconds as set in tools/options/media and I can shrink or stretch it by the various means of doing this - most commonly grabbing the right handle of the gif in the timeline view. When I drop the same gif into v7.3, it has a duration of 100 milliseconds & I can only shrink it - I cannot stretch it more than 100 milliseconds.
As you mentioned it maybe something odd with my gif. I created this new one in the file below today via powerpoint then saving as gif.
https://drive.google.com/drive/folders/18G49TfQUA7e1qW4lqyYLeayZ4V-oM8-6?usp=sharing
Thankyou