Any ideas why this is happening ?

I have two cisco 2610 routers with internal T1 DSU's within them, they
are connected to each other via the T1 DSU using a T1 cross over. I
set up the "circuit" between the two as a PPP on the serial 0/0
interfaces using timeslots 1-2 which should be a 128k circuit.

I have each of these routers then plugged into a switch, one switch
connects to the LAN and the other has a stand alone PC and VoIP phone
hanging off of it.

Communication works fine between everything, LAN to remote PC and VoIP
phone and such.

Now, the question is, I have a PC on the LAN running WAN Killer to the
PC on the other end of the 128k circuit we created between these two
routers. I have it set to like 120% of a 512k circuit, which should
quarantee packet loss or something. I want to see degraded traffic
and problems. While running this WAN Killer I can ping the same
interface WAN Killer is suppose to be slamming with traffic and well
my pings come back perfect with no lost packets.

WAN Killer appears to be doing what it is suppose to however the
routers don't seem to be limiting traffic between the T1 DSU's to
128k, despite having only timeslots 1-2 available.

Any clues as to what I am missing? Should the circuit not be dropping
packets left and right?

My plan is to get traffic to a certain level, and show all the lost
packets and stuff. Then try a voice call and see how bad it works if
it works, then try to implement measures that insure the phone call
will work as planned and the other traffic will take a back seat.