We recently upgrade our hosts from 5.1 to 5.5 and we are no facing intermittent vmotion issues.
vmotion between 5.1 is fine, vmotion between 5.5 is fine but some (not all) vms fail to vmotion from the 5.1 to the 5.5 hosts.
The error is failed with error Connection closed by remote host, possibly due to timeout (0xbad003f.), if I downgrade the host to 5.1 the vmotion works again.
Try to create separate network for isolating vMotion traffic.
Make sure the hostd services on source and destination hosts are fine, run the below command and make sure you are getting an output.
If both ESXi hosts are connected to the same upstream switch, try creating a separate 192.168.x.x class C network to get a different broadcast domain. this will take out any issues with physical network.
test a vmkping across the hosts on newly created vmkernel ports for vMotion. and try vMotion.
you have to disable vMotion on all other ports and have it enabled only on same subnet ports on source and destination.
I have seen this happen in cases where Admins enabled vMotion on dissimilar ports on source and destination.