I have never IVed meth, but im a daily user in the last 12 years.
I got "thick blood" or whatever, same experience as you, becouase of dehydration in the past.
Few times, my blood reacted too (or the substances i mixed in a srynge) and blocked almost instantly the needle... idk why this happened few times, one time i remember to have mixed lidocaine with b12 shot (i do that regulary, becouse i put high volumes in my leg and is little painful without lido), and they got like jelly in the srynge, i cant get out a drop out of that and got somewhat scared, i cant explain this, but happened 2 times...
try to hydrate 45 min. before doing a shot, that helped me a lot when i got thick blood and need to take out blood for lab tests etc