SSH Tunneling doesn't work

[rmd6502]

New Sonic customer, 1gb over AT&T fiber, using a Linksys EA7500 router connected to the AT&T router. The Linksys is in the DMZ from the ATT router, and forwards ssh over non-standard port numbers.
I saw the threads about ssh port forwarding, but that's not the problem I'm having. I'm able to ssh to my home system, but when I try to send any data over port forwards the connection drops almost immediately.
E.g.
ssh myhomeipaddress -C -l me -p 2222 -L 5901:localhost:5900
I get the shell prompt from my machine listening on port 2222, and am able to interact with it, but as soon as I try to connect to VNC I get a few bytes then everything freezes.

[rmd6502]

Actually it seems to happen shortly after any significant number of bytes are sent upstream - I tried catting a large file and only got a screenful or two before the connection froze. Even took out the -C and the port forwards just to be sure, same results.