Lost reverse, need help finding it. 727

On another note, the car runs 11.83 @ 113. People have said the tranny is probably slipping , say the mph is low for the 6500 trap speed.
440, 4000 stall converter, 4:11 spool, 27.8" , tall tire.

All I can really tell you on that is that if a trans slips for 15 seconds it's burned up.
Trans slippage is a misconception among most, in that there isn't nearly enough clutch material or a tough enough material currently to have a trans slip for even a few seconds without burning something.

They are not like a clutch for a 3 or 4 speed where you can slip the clutch multiple times and everything is still fine.
One and done describes an automatic when it slips.
Of course there are instances when a trans slips from fluid being low or a filter being loose, and if caught immediately it can sort of recover from that, but in a race scenario if your trans was slipping it would be a burned black fluid mess before you ever reached the 1/8 mile.
More likely it would be a converter with too much stall or an internal problem in the converter. (IF anything is slipping at all)