92 camaro fuel sending unit

Had to drop the tank and replace the whole sending unit. Now when I get to 1/4 tank or below if I stop fast or turn to quick I run out of gas and the car stalls. What did I do wrong or how do I fix it? While Im at it the ac works beyond great while moving but once I slow down or get into traffic forget it.
Any ideas? Thanks for any input!!

bump

Those sending units do seem to lose calibration when changed out. I guess you have to bend the float arm to get it in range. Way to much work at this point so keep the tank above 1/4 on the gauge. I'd guess you could put an inline resistor in the gauge wire to get it right though, but that's above my head. Is the AC an original R12 system that's been converted to R134? I've seen them warm up at idle when they are overcharged somewhat. I guess the system pressure gets too high on the back side. If so you can bleed some out and help it. I have good luck by putting in two cans of refrigerant, that's only 24 ounces, when doing a complete charge. That's quite a bit undercharged but it seems to work fine, 40 degree air on third blower speed.

Kinda sad on the sending unit because my father in law and I pulled on the weekend not knowing how much they cost. Only place open was the dealer and it was close to $500. Not sure on the freon again because my fater on law did it ,He"s the mechanic in the family. I can change the tank to a 4th gen and he is going to help me build a motor for it. I change that later on and hopefully get things figured out. Thanks for the reply!!