I just put a Hotcam and 2800 Stall in my car and now throughout the whole RPM band it kinda stumbles under acceleration, especially at, or around 35-50mph when it goes into OD. I have an exhaust leak at the Y pipe where the flanges bolt to the headers and Im going to fix that, but wondering if this is possibly a malfunctioning stall, or a combination.
P.S. I also have the car tuned for the cam, but too me it feels more so like the timing is off or something though.

 

I can't really see how the stall can cause hesitation or stumble during acceleration. You say it sounds like timing, did you do the cam work yourself, are you sure the timing marks were lined up? Are to plug wires routed correctly?

Also the exhaut leak prior to the O2 sensor may also cause stumbling, that might be the first thing for you to address, plus on top of causeing bad O2 readings it could also cause false knock. Did you scan the car?