both of those are in the vans skate park right?
the Banzai Drop 3 took me a few tries
Basically when you enter the level, if you go straight you'll hit this unbelievably large garage door, facing the door the clover pool is to your left and forward on the other side of the bleachers. The leaf of the clover closest to where you are standing at the door is what you want to drop into.
you want to start the gap on top of that garage door (what the gap guide guy refers to as "the green thing up there"). I used a different method of getting up there then he did, and I found it a lot easier. While facing the door there's a raised walk way area to your right above the ramps. if you go behind the ramps there's a path that will get you up to the walk way. Above this path is a rail attached to the wall. If you wall plant/wally/grind onto that rail it will lead you up toward getting on top of the garage door. It really doesn't matter how you get up there, just know that you need to get up there.
There are essentially 3 things, the garage door your on, and two pipes next to the top of the garage door on the clover pool side, you need to jump over the first pipe and land in a grind on the second, the pipe will curve around and lead you right to the pool, before it ends jump and pull the trigger to do an acid drop for the gap.
You need to be grinding on that specific pipe for the gap to work.
As for the NO WALLPLANTING! gap, this one took me one or two tries but is pretty easy overall.
I think you're looking in the wrong place. the post with the sign isn't near the humps, it's in the back corner of that area near the corner of the raised walk way. There's a sign about level with the walk way above you that says "no wall planting" with the picture of a skater, if you're facing that sign directly behind you is another post with a tiny little ramp smoothing out the base of the pillar. go up off of that and back down to get some speed, then back towards the no Wall planting pillar and off the kicker in front of it, (I actually did a sticker slap off of it even though the gap guide says you can't), then there is a rail about level with the floor of the walk way, you need to grind on that after slapping the wall. I want to say I tried it once or twice before it registered, and it registered when I did a sticker slap just below the sign.
BTW you can't link directly to GameFAQs articles so you just have to link here:
http://www.gamefaqs....ame/928296.htmlalso if you're having a LOT of trouble this helps
http://thps3.net/THAW/I used it to help with a couple gaps in the ruins and the casino that I just couldn't figure out from the gap guide description.
BTW the hardest gap in the game is easily the last gap in the Vans Park

Oh yeah, and the ONLY level with gaps that you need to get in story mode is the Skate Ranch, every other level in the game you can get all the gaps in freeskate. And don't forget to save in freeskate mode, it wont prompt you to save, nor will it auto save.