A904 issue with stock converter

Been driving my 70 318 swinger with a 1973 a904, tf2 shift kit, fresh ati super f fluid, lokar cable, and a fresh 90's pan/filter/gasket. Twice now while I've been holding at about 45 mph it gives me a feeling like the brakes are being applied(4 wheel manual drum.) 99% sure its transmission related, 1st time it happened I thought the engine was bogging down but it almost seems like 3rd gear holding tighter. I pumped the brakes a bit then I pushed throttle just enough to jump to 2nd and it still has the feeling, after accelerating a bit and letting off the throttle it went away. I turned towards home and now its not shifting to 3rd. The cable is adjusted just tight at full throttle. Anyone have an idea? Something internal? I also changed the 741 for a 489 since it happens last.