Upgrade from Cisco 2500 to 2611 line protocol up/down via IDNX

[R0cky]

Currently running a 2500 with IOS 11.2 via an IDNX. Trying to get a 2611 with IOS 12.3(6a) online. Using a very basic config the serial port comes up and the protocol comes up. Line protocol stays up 27 seconds, down for 3 seconds etc.
Protocol stays up on local and remote loops. Using BGP configured same as my 2500 and "blessed" by the distant end IDNX. It is not a serial port hardware problem. When the 2500 is online I have no problem with line protocol. Using RS530 MT cable that is good. Able to ping my serial port while in both local and remote loops, but not online. I've used two diferent routers and even IOS 12.3(9). Is there some difference between the 2500 and the 2611 that would cause this? I've even got a TAC open with Cisco on this!

 

[R0cky]

Ive done local and remote loopbacks with the following results:
Local Loop
sho int s0/0
Serial0/0 is up, line protocol is up (looped)
Hardware is PowerQUICC Serial
Internet address is 198.26.152.66/30
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation HDLC, loopback not set
Keepalive set (10 sec)
DTR is pulsed for 1 seconds on reset
Last input 00:00:06, output 00:00:06, output hang never
Last clearing of "show interface" counters 00:05:18
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
448 packets input, 603232 bytes, 0 no buffer
Received 32 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
448 packets output, 603232 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 output buffer failures, 0 output buffers swapped out
0 carrier transitions
DCD=up DSR=up DTR=up RTS=up CTS=up

Remote loop
sho int s 0/0
Serial0/0 is up, line protocol is up (looped)
Hardware is PowerQUICC Serial
Internet address is 198.26.152.66/30
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
reliability 252/255, txload 1/255, rxload 1/255
Encapsulation HDLC, loopback not set
Keepalive set (10 sec)
DTR is pulsed for 1 seconds on reset
Last input 00:00:06, output 00:00:06, output hang never
Last clearing of "show interface" counters 00:03:01
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
426 packets input, 602464 bytes, 0 no buffer
Received 18 broadcasts, 0 runts, 0 giants, 0 throttles
13 input errors, 6 CRC, 7 frame, 0 overrun, 0 ignored, 0 abort
426 packets output, 602464 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 output buffer failures, 0 output buffers swapped out
0 carrier transitions
DCD=up DSR=up DTR=up RTS=up CTS=up