Kinda wierd issue..... car picking up the worse the air is

My 69 Dart street strip car made its second outing of the season this weekend. First really, initial outingwas rain shortened, three passes total
Anyhow car has been about a tenth and a half off from where it was last season. I am factoring in conditions when i say that. Little bit everywhere on the slip.
First outing three passes
Nine passes this weekend.
Every single pass the car has made it has continued to pick up. Yesterday we got only one time trial. About 10 in the morning. I add three on it as first round was 1 in the afternoon. I always drive the car around a good bit to warm it up, and the car always enters the water box at the sane temp.
So first round, much hotter, instead of falling off a little car picks up 3 out of nowhere. I got beat.....
Bought back in. Now its 4:30 in the afternoon. Its hot, we are seeking shade.
I put 2 extra on it from the earlier pass, figuring the car has to back up in the heat.
Nope picks up two this time. Got me stumped. So a 9 flat car beats me. Sucky day for the driver. Not gonna lift on a 150mph car coming at me.
Put new plugs in this morning. Hard to tell much but it definitely a little fat. I drive the car. Need to pop in one new plug and make a pass and check
Plan to pull a couple jets out of the front and back
So now, after a dozen passes on it, car is probably about half a tenth from normal.
Have no clue why its picking up in worse air, and why it is taking some passes to come around.
Last year on a typical summer day car wouldn't move around more than one, maybe two, racing it from morning to late night.
Any ideas?