Weekend started out good, ended early and not so good

Went 10.58, 6.70 in the 1/8.
next morning it went 6.64 in the 1/8, probably a 10.48 or maybe 10.49.
Picked up 2 tenths over the old best, with the only change being headers.
the air was good, especially Saturday morning, but not mineshaft. It was in better air when it ran its previous best.
now it’s down with broke tranny
That is a HUGE gain!! High five! Now get it apart and tell us what is wrong please.