First Post. Appreciate any help.
Will try to provide complete and accurate info.

Problem: Pressure tank does not completely fill.
Pump Runs 20 seconds
Pull Down 2.5 gallons

Pump: McDonald 21050k2a in-well 10 GPM

Weltrol WX203 36 Gallon 30psi-50psi Switch
Air setting 29psi

Well is 160 ft. 22yrs old.
Replaced Weltrol 202 yesterday.
Old 202 was running 15 seconds and giving 3.5 gallons between pump cut-off and cut-in. Air at 17psi when removed.

Installed a slightly used larger Weltrol 203. Kept old pressure switch. Checked air charge at 29 psi. Pump runs 15 to 20 seconds.
After cut-out at 50psi pressure bounces to approx 37psi.
Draw down was 2.5 gallons before pump cuts in again.

Tank does not feel like it is heavy or full. Cannot notice any condensation or colder section of water.

Any ideas? Opinions? Suggestions on what to test/expect????
Total Surprise that different tank did not solve issue.

Goal is to get pump to run longer and have a larger buffer/draw down like I think it is suppose to have.

Not a pro at this, only a homeowner who needs to know his water is safe and running correctly.

Thanks for any help.

Bob P