Ok. I've always had best luck, then bought the tools, to stuff them rather then cut lengthwise. I have the jalapeno coring tool, which looks almost like a potato peeler, which cleans it out of the seeds and membrane. I use the jalapeno popper racks to hold them vertically.
I'll give you the details on how I make them usually, and they would be the ones you tried.
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This is my basic set up. I never precook the peppers. I also don't poke a hole in the bottom. That's been suggested a few times. Mine has come out better without the oil dripping out.
All i use is the raw jalapeno, cream cheese (regular not whipped), block cheese (whatever you prefer, I use Tillamook pepper jack or cheddar), and thick cut bacon. I cut the bacon just long enough to cover to top with enough over hang to pin it with a toothpick. I use a piping bag (or you can use a plastic bag with edge cut off or spoon in with a butterknife) to fill 1/2 way with cream cheese. I cut the cheese into long enough pieces to fill peppers about halfway and squared around enough to just fit into the opening. Once the cheese is in then I backfill the pepper enough to fill it the rest of was with cream cheese. Put bacon over the top, pin, then cook. I like the low and slow at around 225 until the bacon starts to get crusty. Pull from oven/smoker and let it rest.
If I'm adding a protein inside (shrimp, crab, sausage, etc) I'll do filling a little differently. I'll grate the cheese, chop up the protein to smaller chunks (I'll precook the raw proteins first) then mix all the cheese, protein, and cream cheese together in a bowl first, then pipe into the pepper. Then add bacon and cook like I do with a normal pepper set up.
Here's what they look like when I first put them in
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And the finished product
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