Watch the Descending Swing online guitar lesson by Jasper Mortier from 50 Blues Bass Licks You Must Know
This lick is a Blues Rock Swing Style Groove. Stevie Ray Vaughan - like Jimi Hendrix - liked tuning his guitar half a step down to Eb to get a fuller sound and a different feel on his guitar. At the same time he used thicker strings than regularly. If you've got to play a whole repertoire with a guitarplayer doing this, it's easiest to tune down too since often songs will be played in open string tunings like E and A. So that tuning would be Eb Ab Db Gb for a 4-string. If you're serious about this I suggest you get thicker strings too to get it more tight.