Router-to-router connection issues

Greetings:

Since my cable connection comes into my house in the basement, Ive modified my home network configuration by adding a router in the basement so that I can move my wireless router to an upstairs room to get better coverage. The new configuration looks like this:

Primary Router:
    Workstation 1 (Wired Connection)
    Secondary Router:
        Workstation 2 (Wired Connection)
        Laptop (Wireless Connection)

This all generally works, but Ive noticed a decrease in speed and reliability of the network. Occasionally, the connection of the computers connected to the second router is effected by the connection of the computer connected to the primary router.

Any suggestions would be appreciated. The router models and configurations are listed below.

D-Link DGL-4100 (Primary Router)
Router IP Address: 192.168.0.1
Enable DNS Relay: On
Enable RIP: Off
WAN Mode: Use DCHP
Use Uni-casting: On
Enable DCHP Server: On
DHCP IP Address Range: 192.168.0.100 to 192.168.0.199
Always broadcast: On
Add DCHP Reservation: Off
Number of DCHP Clients: (Shows correct number)
Virtual Servers: None
Enable GameFuel: Off
Enable SPI: On
UDP Endpoint Filtering: None
TCP Endpoint Filtering: None
Non-UDP/TCP/ICMP LAN Sessions: Enabled
Enable UPnP: On
Enable Ping Response: Off
Enable Multicast Streams: Off

Application Level Gateway (ALG) Configuration
PPTP:  Enabled
IPSec (VPN): Enabled
RTSP: Enabled
Windows/MSN Messenger:  (automatically disabled if UPnP is enabled)
FTP: Enabled
H.323 (NetMeeting): Enabled
SIP: Enabled
Wake-On-LAN: Enabled
MMS: Enabled

WAN Status Shows:
Connection Type : DHCP Client  
Cable Status : Connected  
Network Status : Established  

LAN Status Shows:
IP Address : 192.168.0.1  
Subnet Mask : 255.255.255.0  
DHCP Server : Enabled

LAN Computers:
192.168.0.135 (Wired connection via secondary router)
192.168.0.135 (Wireless connection via secondary router)
192.168.0.199 (Wired connection via primary router)


D-Link DIR-855 Wireless (Second router)

Router IP Address:  192.168.0.2
Enable DNS Relay: On
DCHP Server: Off
Connection Type: Auto-detect
Enable Traffic Shaping: On
Automatic Uplink Speed: On
QoS Engine: Off
MAC Filtering: Off
Access Control: Off
Enable SPI: Off
UDP Endpoint Filtering: Address Restricted
TCP Endpoint Filtering: Port and Address Restricted
Enable UPnP: On
Enable Multicast Speed: On

WAN Status Shows:
DHCP Client
QoS Engine : Inactive
Cable Status : Disconnected
DNS Status : Offline
Network Status : Disconnected
Connection Up Time : N/A

LAN Status Shows:
IP Address : 192.168.0.2
Subnet Mask : 255.255.255.0
Auto IP Address: 0.0.0.0
Default Gateway : 0.0.0.0
Primary DNS Server : 0.0.0.0
Secondary DNS Server : 0.0.0.0
DHCP Server : Disabled