You say the system does not lose pressure unless someone turns on a faucet, so your foot valve is OK. The tank is holding the air charge so it is OK. Then you say when the shower is used, the pump never shuts until water usage is halted. Which means your pump is running continuously instead of cycling on and off, which is a good thing. I guess I don’t see where you think the pump is short cycling. Is it just bouncing on and off quickly when the pump starts or something?