ecu learning and Towing. Does this seem right?

Per Scangauge readings.

Pre towing - MPG average per my route to work - 21MPG

Towing trip - 4000lb Trailer for 200 miles in 4th gear - 11MPG avg

For the next two weeks after towing - MPG average per my route to work - 14MPG (And black tail pipe)

1 week ago reset ecu to see if it would help - Two days after reset my average per my route to work - 21MPG again.

Why would I need to reset the ecu after towing?

 

Weird. I get about the same mpg when I tow, but mpg goes back up when I lift the trailer.

 

I didn't have this issue for shorter trips. This was the first 200 mile trip.

 

11 MPG is about right for 4000# I tow a lot and as soon as I park the trailer the mileage goes right back up just dropping my towing speed make an immediate difference. I can follow it with the Scan Gauge and it's pretty damn close when I fill it on pen and paper. It's not unusual for me to do a 500 mile trip.