89-740 fuel sending unit

89- 740 GL wagon I recently had my fuel sending unit replaced and now once I fill the tank the gas gauge takes a good 45 minutes of steady driving to reach full. Also I seem to only be able to use half a tank of gas once the gauge reads empty the tank is still half full but the car stalls as if the tank is empty. I know the tank is only half empty because it only costs $25 to fill it up. Is the new sending unit faulty or does it just need to be repositioned in the tank?

Thanks in advance Rob