Question : Problem: Layer 3 Ethernet Switch Routing

My question is about routing in layer 3 switches.  There are three switches involved, all are Cisco.  Two 3750 switches hang off of a 4506.  The 3750 switches have two vlans using the same number scheme, but are on different subnets.  There is no real router involved only the layer 3 routing capabilities of the three switches.  Is there a way to route packets from one 3750 to the other via the 4506, w/o having to use two ethernet ports per switch.  Packets from say vlan 5 that with say subnet 10.10.10.0/24 to vlan 5 on the other 3750 which has a subnet of 10.10.20.0/24, packets from say vlan 20 10.10.30.0/24 to vlan 20 on the other 3750 vlan 20 10.10.40.0/24.  Again with only one port per.  The thought of sub interfaces with dot1q came up, but I had read that is not supported on these devices fastether/gigether ports.  Would appreciate anyone who could shed some light.
Thanks

Answer : Problem: Layer 3 Ethernet Switch Routing

All correct. The reason that duplicating vlan numbers works is that on the 4506, you're using routed ports. So the 2 3750s never interact at Layer 2 and the vlan numbers don't matter.