Weird, sudden AFR issue Proform 750cfm!

Needle and seat on the float may have crap in it. Same with air bleeds. A .031 to .037 is a huge jump and way out of the norm.
Move the IFR to the bottom and readjust the idle circuit. 20 to 50 mph you are mainly on the idle circuit. Moving the IFR to the bottom stabilizes fuel flow in the Idle circuit which is where a street car mainly operates. 4 emulsion holes open, what size are the openings? 2 .026 is all you need. If you have 4 hole blocks run #1 & 3 .026 and block off 2 & 4.
O2 sensors read O2 and can give false readings off what is really happening in a cylinder. As an example, a plug misfire allows more O2 to be seen at the sensor, you think you are lean by the AFR gauge.