Anything over 3iu per shot makes me lethargic as f*ck too. I did 10iu a day for a couple weeks and basically I couldn't function without a boatloads of stimulant (caffeine, ephedrine..). Now I only do 10iu, one shot pre workout M-W-F, with regular pre workout with added DMAA. No lethargy with that and believe it or not results better than 5-10iu ED spreaded 2-3 times a day
Are you using slin with 10iu pre work out?