The problem with pickles is that I think the sugar actually has some
function in it, as to helping with the process of making the vegetables
involved, actually become pickled.   Otherwise I cannot imagine why it is so
hard to find sweet pickles made with a sugar substitute like Splenda.

You could experiment with a few different kinds to see if you could doctor
it up to some acceptable flavor.  You may end up throwing a few batches
away, but maybe you will luck out eventually.   Sour pickles usually have
lots more salt and different seasonings than sweet, so that could be a clue
as to why your current batch didn't turn out right.

As for tuna salad,.... I use chopped celery, chopped sweet onion,
mayonnaise, black pepper (rather generously) and my secret ingredient which
seems to make the whole thing taste great,  a tablespoon of cider or white
vinegar.    I have never used sugar in tuna salad and everybody always likes
my tuna salad a lot.

Another dish which I discovered actually NEEDS to have some sugar in it, is
coleslaw.   For some reason the cabbage doesn't wilt properly without it.
Fortunately, when the cabbage wilts, the dressing ends up mostly in the
bottom of the dish, so I have made that little concession and will eat
coleslaw but squeeze most of the dressing out of my portion.  Come to think
of it, that may be why the sugar-free food industry hasn't caught the wave
with pickles yet.  Maybe it helps them wilt too.