Check out John Lindgren on this site and learn the final fantasy arps he has...take it slow and practice on that...it will help.

here is the link if your feeling lazy
http://guitartricks.com/freelesson.php?input=YjA6YTJjajs=

Also,alternate picking arps IS a great way to improve you alt picking accuracy and speed...keep it up!

Just remember to lift your fingers after striking the note to make it 'clean'...if the arp/sweep makes it so you have one finger on multiple strings,try 'rolling' that finger off the notes as you pass them.

Good luck dude!