Do I need a new converter?

Do this test......
Motor/trans all warmed up.

With the car going along at 10-15mph, trans in high gear, with the motor just above idle(12-1500ish)......... floor the gas.
The tax needle will swing right up to some rpm and then hold steady for a bit.
Whatever that number is, that’s the effective stall speed for that converter, behind that motor, in that car.
The “flash” stall speed.

If I were chasing ET, for that combo I’d want at least 4200-4500 flash stall speed.
It’s going to take a pretty good 9.5” to get you there, and still have decent efficiency out of the converter.