I found a lead player who could shred hard and arranged a jam.
He's timing was terrible and when it came to simple rhythm parts he got worse.

Maybe not everyone is so bad.

Once I started recording and doubling my parts I felt ashamed at how poor my timing was.

This was my problem too. My shitty town's shitty music store never sold metronomes, and so they never even crossed my mind until I bought a multi effect modeling processor that had a built in metronome. The thing is, you never know until you really pay attention. I've been practicing with one basically every night for a while, and it's vastly improved my playing and timing. About the topic though... Almost every technique that you start to learn is difficult at first. They get easier as you practice though. I'd have to say the hardest and most frustrating ones are sweep picking, speed picking, hyper-speed down strokes, and big/technical string skipping.

Playing actual solos is harder than 17 finger tapping in hybrid minor...

well i think the hardest is stuff that most metal guitarist's don't do. I began guitar learning easy folk songs and then some guitar finger picking and alternate strumming techniques so to me thats the easy stuff. i haven't had anyone show me or expain to me what the sweep picking is or how to get pinch harmonics. so for me that would be the hardest.

Other than some tritone sweep I always do on the three high strings I cant sweep at all. Pinch harmonics are hard until you get it down then they're rather simple. For me playing without adding 6000 minor 2nds in every riff is the hardest thing.

I'm still having a bitch of a time with not ringing out on 3 string and 5/6 string sweeps. It's getting better for sure, but I have no idea how the other guy said he could do it for 5 years and still suck at it. I've been at it a few months and I can go 110-120 bpm 16th note sweep on 6 strings with little effort :/

Still, sweeping is my only goal. After that I don't care, I've gotten to where I want to get.

Pinch harmonics are really hard when you first learn them, but then it "clicks" and you will never have problems with them again. But sweeping is like playing the guitar itself...you always feel that you aren't good enough and you always want to get better.

Sweeping, depending on what chord you use because some chords are very simple to sweep. sweeping difficult chords and intigrating tapping into the equation is extremely difficult

I am not a big lead guitarist, but I want to be. The problem is learning what scales and notes to play. I am taking Music Theory next year, but that won't help me that much. I can play pretty fast, but whenever I do, its random crap.

I honestly don't know what most of these terms mean. Tapping, in my experience, though, has been a bit tough to get right.
I don't use a pick, so I'm not sure how much harder pick-sweeping is than regular sweeping, which I'm assuming means moving fretting fingers directly in line with picking fingers, which seems rather hard to me.

sweep pick

Straight sweeping is easy- string skipping is hard.

my favorite guitar technique is ...let me tell you took me five years to master inside the circle of 4th (i play everything i learn inside the circle of fourth this way i can play something meledic and structured befaore i destoy and make it my own)
it's call sweep finger tapping (no picking just tapping) aka double arpeggios taping (difference is you are not always using arpeggios)
it's really hard and demand a lot of practice (years)
nice sweeps are nice when done a nice speed
but this technique is just incredible
it evolve around plaing 1 mode with one hand and another with the other
8 finger tapping may be needed for high speed
understanding of scales arpeggios and chords
should be more the understoud
people i foundout that were using similar technique or the same thecniques are dave celentano and micheal angelo batio other the that i have not a single clue clue

you got it all wrong but (you don't need guitar lesson if you can teach your self )
guitar theory is where it's at scales and chord that what theory is allabout and it's what melodies are made of

instead of taking guitar lesson buy some theory book or at least check some out (playing fast mean nothing when you don't know what to play)

here are my favorite in order

1. Arpeggios by: Joe Charupakorn
2.guitar grimoir by: Adam Kadman (three diffrent books)
3.chord connection by: robert brown

I havent been playing guitar for that long but so far what ive found hardest is hammering and sliding at the same time. I havent tried any of the fancy techniques though.