Cisco 877 performance problems

Hello,

I have a bit of an annoying problem with a Cisco 877 that I cannot seem to get to the bottom of. Last week I changed the config of the ACL on my Cisco 877 to try and improve security, as the previouse ACL on there, that someone else created, was very lax. The next day however, a new problem started to occure. After a few hours, web browsing slows down to the point where most pages stop loading. Other services, such as smtp still seem to work ok though over the same link. If I then do a reload on the router, everything works perfectly again for a few hours, and then the problem returns. My ISP is Demon Internet, the line is ADSL, and I have posted the 2 ACLS below. The first one is the config that was running, and the second is the one that is running now. ACL 100 is applied on Interface Dialer0 IN.

Old ACL

access-list 100 permit tcp any any eq 443
access-list 100 permit ip any host xxx.xxx.xxx.xxx (public IP removed)
access-list 100 permit icmp any any administratively-prohibited
access-list 100 permit icmp any any echo
access-list 100 permit icmp any any echo-reply
access-list 100 permit icmp any any packet-too-big
access-list 100 permit icmp any any time-exceeded
access-list 100 permit icmp any any traceroute
access-list 100 permit icmp any any unreachable
access-list 100 permit udp any eq bootps any eq bootpc
access-list 100 permit udp any eq bootps any eq bootps
access-list 100 permit udp any eq domain any
access-list 100 permit esp any any
access-list 100 permit udp any any eq isakmp
access-list 100 permit udp any any eq 10000
access-list 100 permit tcp any any eq 139
access-list 100 permit udp any any eq netbios-ns
access-list 100 permit udp any any eq netbios-dgm
access-list 100 permit gre any any
access-list 100 deny   ip any any

New ACL

access-list 100 permit tcp any any established
access-list 100 permit tcp any any eq smtp
access-list 100 permit tcp any any eq www
access-list 100 permit tcp any any eq 1723
access-list 100 permit tcp any any eq 443
access-list 100 permit udp any eq domain any
access-list 100 permit gre any any
access-list 100 permit icmp any any
access-list 100 permit udp any eq bootps any eq bootpc
access-list 100 deny   ip any any

Can anyone tell me if they think this problem is related to this ACL config, is a router fault or an ISP issue.

Any help much appreciated.

Robert