Our well water pressure seems lower than usual in shower, outside sprinkler, etc. Pump turns on at 40 and off at 60. But after pressure reaches 60 it decreases to 40 even if no faucet or other water appliance is on. Is that normal or do I have a well problem? Pressure tank air pressure looks good at 40.

There are two possibilities:

1. A leak somewhere between the house and tank... not likely though since it would not tend to stop at 40. Still, if you have cutoff between the house and the tank, turn it off and see if pressure holds or continues to drop. If it holds, then you have found your problem.

2. A leaking/malfunctioning check valve. That would be my guess in this case. It should not allow any backwards flow into the well at all. Yours may be letting pressure drop down to 40 and then holds. You should have a check valve between the pressure tank and the well head. See the site below to learn more. But be aware that you might also have a checkvalve above the pump in the well (assuming that you have a submersible pump).

Also, your tank pressure at the air valve at the top should be 38#.

Water system check valve location & purpose - private pump and well system do-it-yourself repairs (http://www.inspect-ny.com/water/CheckValves.htm)