I write from an ubuntian perspective so you may need to translate into RedHatish.
Check that network, portmap and nfs-common init scripts are called before mountall.sh; if they are not, the only thing that makes NFS mounts in /etc/fstab work at all is that NFS keeps trying long enough for the network to come up later.
One possible cause of the network coming up slowly is switches which may queue certain types of packets (I say "certain" because I'm not
certain which!). I've seen similar threads in which the solution has been to re-configure Cisco switches.
There may be timeouts available on the NFS options in /etc/fstab which you could extend.
Another solution may be to remove the NFS entries from /etc/fstab and to program their mounting into a later init script like rc.local.