I realized that my technique is sloppy and my playing feels tiring because my picking hand is way behind my fret hand technique wise. So, can anyone recommend lessons, excercises, or helpful advice in efficiently developing my picking hand accuracy and stamina? I'm otherwise an experienced guitarist, and I grasp concepts and techinques relatively easily (i.e. I'm not even close to a beginner), so even "difficult" excercises should be good.
how beginner are you? what kind of songs are you playing at the moment (or trying to play)
I'm also spending some time working on my picking. I'm coming off a couple of years without playing much, so I'm working on bringing everything back up to snuff. I'm going about it by making sure that I spend time on each of the following each day:

1) A 3 note per string lick. I'm currently doing an exercise suggested by Rusty Cooley a few years ago in a guitar mag. He calls it "split modes", but basically you take the major scale, play the first 12 notes all 3 nps, which takes you up to an octave and a fifth. Then you back up to the octave, and repeat the 12 notes from there. Then do the same thing going down. Then you shift up the neck and play it the next position starting on the 2nd note of the major scale, and so on. I spend about 5-10 mins on this as part of my warm up.

2) A 2 note per string lick. Obviously the minor pentatonic works real well for this. Throwing some kind of sequence in there just adds to the fun. A great one is the opening run in the solo of Technical difficulties. I've also come up with a neat sounding 3 octave 2 nps arpeggio that I'll play for practice. I'll play (in the open position) E-F-A-C, then shift up the neck for each octave. Then in the 5th position, I'll switch the intervals and do A-C-E-F, then back to the original intervals in the 7th position (B-C-E-G), and 12th position. It's a lot of fun and a challenge for the left hand.
One thing about the 2 note per string licks. I'll alternate whether I start on an upstroke or a downstroke (using on alternating days). I'll also play them with different note groupings (16ths, 8th note triplets, and 16th note triplets). This really helps with your picking and synchronization as you are developing the control necessary to accent in different places and not just let the strings decide where your accents should be.

3) A short stationary lick that can be looped, that has lots of outside picking. This is to home in on just the picking. I have one quick lick I play in 16th note triplets that's 12 notes long. The first 6 have an inside cross and an outside cross, and the second 6 are on one string. The idea of arranging it like this was to help with combining the small movements you make in picking one string with the wider movement you do when crossing strings. Another great lick for really working on outside picking is Paul Gilbert's "Piano lick". Do a search for it on youtube. It is absolutely brutal, and it's a great pinky workout as well.
Another great lick for improving your string crossing is the opening rhythm of Paul Gilbert's Technical Difficulties. It sounds amazing and is very enjoyable to play, and it gives your picking technique quite a workout.

Hope this helps!
I'm not a beginner at all I can play things like the intro of "in the presence of enemies pt.1" effortlessly and also stuff like gojira and opeth. And I can economy pick, but occasionally prefer not to.

And thanks se-randomnumbers, that helps a lot
^ lol @ random numbers. It's the date my wife and I met 01/21/01 Anyway, I'm glad the suggestions helped!
Cool man, good luck! I hope it helps. I really like Gojira, btw. They opened for slayer when they played here in Dallas in November, and it was my first time hearing them. I was really impressed. They rock.