JJ1 Incomp3t3nc3
 

I know this isn't JJ2, but I think this is about the only place I'll actually get useful advice.

In JJ1, I can't get more than 98% of the items in Tubeletric 2, 84 and 44% in Jungrock and about 50% in Sluggion. I've played the levels over and over, but I can't find the rest of the stuff, and I'm too much of a perfectionist to give up.

*tries out*

If I recall correctly, it is possible to get 100% in Tubelectric. It's kind of hard to help you though, since we can only guess which item you might have missed. You should always watch out for the dastardly "items-that-appear-long-after-you-passed-them" bug.

I have stopped trying to get all items in Jungrock and Sluggion a long time ago. Those levels just look bugged to me. The Jungrock guardian level sort of proves that point (20% enemies upon killing the big lizard, whereas all other episodes give 0% or 100% in their guardian levels)

All else fails you can always open the level in JCS94 and scour it.