C-6 trans output shaft locks up when going into second...possible causes ??

I was racing my 460 Turbo Coupe (with a C-6) last night and on one run it launches as normal but when the trans went into 2nd, alot of noise came from the trans.
I pulled to the side but did not see any fluid leaking.
I drove back to the pits slowly.
What I found out is that 1st works fine as normal.
Reverse works fine.

When the shifter is in "D" the trans works fine until it goes from first into second and then the driveshaft locks up. If I put the shifter in "2" the trans locks up like forward and reverse are locked together.

Any ideas on the possible causes ?

Could have a seized reverse clutch but with the noise, you likely have a broken planet. It will have to come to know.