Try the following substitutions.
T 2/28 - SEA-OAK AS - OAK-RNO WN - RNO-LAX WN
W 2/29 - LAX-BOI UA - BOI-LAS WN
adds 236 miles.
S 3/10 - ORD-BHM UA - BHM-BNA WN
S 3/11 - BNA-ECP WN - ECP-ATL DL - ATL-FNT FL
adds 335 miles.
S 3/18 - PHL-ALB US - ALB-JFK DL - JFK-BOS DL
adds 129 miles.
Add a day in BOS or finish a day earlier.
Using the same calculator as your original, this comes to 25,104 miles. I checked schedules for all the days where I made changes and they all work with 3 hours or more between flights.