Sounds like you had a fine time of it, all things considered...
You are so right about crosswinds slowing you down....
My little pushrod 350 will lose 5+ mph if it just sees a flag move anywhere in the area....
Man, that is a LOT of slippage you had,,,, 20% or so,,, that backend would have been fishtailing all over the place, and the tire should have been all chewed up...
DO you think some of it could have been clutch slippage? I had that problem and I had to shim the clutch springs to get it to stop...and then, of course, the dang clutch cable failed from all the extra strain....on the starting line and with no spare on-hand...that's racing
It will often only show up in High Gear and after the oil get good and warm.....You are ,after all, making a lot more horsepower than an oem motor....
Good fortune and hope to see you on the track sometime..