Need some input for a 2bbl problem

[Sam Capizzi Jr]

Hey guys Any help would be appreciated. I have a 318 2bbl that wouldnt go past 5000 in Pittsburgh. I went to my local track and went 8.65 shifting at 5400 5600 no problems the week before. Normally The car stops pulling at about 5800 in good air.
My first three passes in were ok 8.79 8.79 8.80 at AA of about 4000 70% humidity, temp 80 and baro 28.60 Then as the air gets worse the car started falling off 8.82 8.91.
Then the next day the air was about 4400 feet baro 28.40 and temp 86 .. The car would get to 5000 and act like it was floating the valves and layover then I would shift and it would start pulling again and went 9.05. Next pass same thing 9.12. Then 8.93 short shifting it at 4800.

So after all that rambling is it possible the bad air would be the cause of all my problems. The timing is at 30. Plugs perfect. I checked valves perfect. No loose grounds. Wires ok. I'm lost and new to this two barrel thing.
Thanks Sam