When the PSeries routers are connected to an actual T1 circuit they derive their clocking from the network. However, since you are testing the PSeries routers back to back via a T1 crossover cable you will need to build the following cable and also change the Clocking on one of the routers to "internal".
Cable diagram for T1 crossover
RJ45 RJ45
1 --------- 4
2 --------- 5
5 --------- 2
4 --------- 1
Note: pins 1 and 2 are for receive ( 1= ring, 2 = tip). pins 4 and 5 are for transmit (4=ring, 5= tip)
Change one of the PSeries routers for "internal" clocking.
From the main menu, select Configuration / Wan Set-up / Link set-up / T1/E1 Set-up / Clocking [internal]
After testing, make sure you change the Clocking back to "Network" when you connect it to a true T1 circuit.