Bad ping times to router, regular as clockwork

For the past couple of days, my LAN and WAN network connectivity on my MBP has badly degraded. A quick ping to my router (a Linksys WAG354G) reveals the likely source of the problem: 5-6 good ping times followed by 2-3 bad ones, regular as clockwork:

PING 192.168.1.1 (192.168.1.1): 56 data bytes
64 bytes from 192.168.1.1: icmp_seq=0 ttl=255 time=1.624 ms
64 bytes from 192.168.1.1: icmp_seq=1 ttl=255 time=1.664 ms
64 bytes from 192.168.1.1: icmp_seq=2 ttl=255 time=1.607 ms
64 bytes from 192.168.1.1: icmp_seq=3 ttl=255 time=1.871 ms
64 bytes from 192.168.1.1: icmp_seq=4 ttl=255 time=1.628 ms
64 bytes from 192.168.1.1: icmp_seq=5 ttl=255 time=1749.691 ms
64 bytes from 192.168.1.1: icmp_seq=6 ttl=255 time=2060.993 ms
64 bytes from 192.168.1.1: icmp_seq=7 ttl=255 time=1064.956 ms
64 bytes from 192.168.1.1: icmp_seq=8 ttl=255 time=65.077 ms
64 bytes from 192.168.1.1: icmp_seq=9 ttl=255 time=1.409 ms
64 bytes from 192.168.1.1: icmp_seq=10 ttl=255 time=1.827 ms
64 bytes from 192.168.1.1: icmp_seq=11 ttl=255 time=1.826 ms
64 bytes from 192.168.1.1: icmp_seq=12 ttl=255 time=1.670 ms
64 bytes from 192.168.1.1: icmp_seq=13 ttl=255 time=1.803 ms
64 bytes from 192.168.1.1: icmp_seq=14 ttl=255 time=1.993 ms
64 bytes from 192.168.1.1: icmp_seq=15 ttl=255 time=3216.875 ms
64 bytes from 192.168.1.1: icmp_seq=16 ttl=255 time=2216.855 ms
64 bytes from 192.168.1.1: icmp_seq=17 ttl=255 time=1217.869 ms
64 bytes from 192.168.1.1: icmp_seq=18 ttl=255 time=218.826 ms
64 bytes from 192.168.1.1: icmp_seq=19 ttl=255 time=1.646 ms
64 bytes from 192.168.1.1: icmp_seq=20 ttl=255 time=1.815 ms
64 bytes from 192.168.1.1: icmp_seq=21 ttl=255 time=1.668 ms
64 bytes from 192.168.1.1: icmp_seq=22 ttl=255 time=1.807 ms
64 bytes from 192.168.1.1: icmp_seq=23 ttl=255 time=1.764 ms
64 bytes from 192.168.1.1: icmp_seq=24 ttl=255 time=1.659 ms
64 bytes from 192.168.1.1: icmp_seq=25 ttl=255 time=3315.282 ms
64 bytes from 192.168.1.1: icmp_seq=26 ttl=255 time=2315.046 ms
64 bytes from 192.168.1.1: icmp_seq=27 ttl=255 time=1316.318 ms
64 bytes from 192.168.1.1: icmp_seq=28 ttl=255 time=316.798 ms
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The symptom persists whether I connect wired or wirelessly to the router, which I've both rebooted and factory reset to no avail. Other machines (Mac and Windows) on the LAN are having no issues whatsoever. I don't believe the the problem exists in other locations (e.g. my office), but I'll double-check tomorrow.

Any suggestions?