T56 weirdness - 6th gear 1:1?

[rpoz20]

Yesterday I looked at an LS1 T56 I was considering for an LS3/T56 swap into my 69 Camaro. When I was confirming the gear ratios by turning the output shaft and counting the turns of the input shaft everything checked out until I got to 6th gear. Instead of .5 turns of the input shaft for one turn of the output, 6th gear gave a full turn of the input for a full turn of the output (I.e. 1:1). Any ideas on why this would be the case? The trans had apparently been used in a drag car and had been built by 6-Speed Inc. (now out of business).