i've recently started using Gonzales reeds, recommended by my teacher, and one thing i really like about them is that they come in quarter steps. i bet some other brands of reeds do the same too, you might want to look into trying others.
if you want to try gonzales reeds, (you might have to order them online, i know my local store doesnt carry them. i got them through amazon) they supposedly run a half step lower than vandorens. I use a three vandoren but a 3.5 or 3.75 gonzales...

it might not be the reeds, but could be something dented on the clarinet. it could just as well be the reeds. i would suggest switching to a different brand like mitchell lurie. i use a 3.5 and find it works fine, but im not sure how the 4s would work.