I have a 2010 F150 with 150K miles. This is a lot of miles on a transmission. Dealer says I or they should change fluid by dropping pan and replace trans filter.

You are way overdue for a fluid and filter change. Consider yourself luck to have made it that far without the trans dying.

Don't let them talk you into a flush!

Yes that is a lot of miles without changing the trany fluid and filter. It makes it a lot of miles on the trany now since the maintenance has not ben kept up with.

Your owner's manual indicates a change at about 90K miles. That is bull. A relative owns his own tranny shop for 45 years. Told me in the early 70 to bring him my car every 40K to have the filter and fluid changed. My oldest F 150 is a '96. Never have one bit of trouble with any vehicle I have owned (transmission wise) by changing the fluid every 40K.