What's going on? Migration question.

I'm still trying to migrate from a new Elite Pro enclosure (usb3) with a superduper clone from a 21.5 2010 iMac to a 21.5 2017 4k iMac. I've tried various ways including a reinstall of 10.13.2 (the 2010 iMac and clone has the same OS). The migration (with migration assistent) starts off o.k. with a message saying " migrating documents at 49 mb/s about 24 minutes to go". But then it seems to stall by about 8-10 minutes to go. Last night i let it continue for about 5 hours to no avail so i had to break the process off. I must have tried this operation 6-7 times including several new installs of the OS so i'm starting off with a virgin iMac so to speak. It's driving me slowly but surely insane. Does anybody out there in the community have an answer? .Please