1. I have difficulty/trouble in remembering names.

2. 1. I have difficulty/trouble when I remember names.

(Are both the same and interchangable?)

2 answers

1. I have difficulty/trouble in remembering names.

2. I have difficulty/trouble when I remember names.

3. I have ______ remembering names.

(Are both the same and interchangable? Can we delete 'in'? Do you have some other words which can be put in the blank as in #3?)
I think they mean slightly different things.

1. This one means that you have difficulty with the skill of remembering names.

2. This one means that once you have remembered a name, you have difficulty with something else.