1965 727 won't shift into 3rd

Does it just rev up more and more and not shift?
Does it have engine braking when it won't shift and you let off the gas, or just coast like it's in neutral until it gets back down to a speed where you feel second again?
When i rode it it before all the upgrades, didn't feel like neutral, felt like braking like it was in low 2 and not drive. In drive he would go wot then let off and it would eventually shift.